[SYCL][Doc] Add test plan for dynamic linking feature

SYCL/TestPlans/DynamicLinkingTestPlan.md

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+# Test plan for dynamic linking of device code
+
+This is a test plan for device code dynamic linking feature described in
+https://github.com/intel/llvm/blob/sycl/sycl/doc/SharedLibraries.md document.
+
+## 1. Testing scope
+
+### 1.1. Device & BE coverage
+
+All of the tests described below are performed on Intel CPU and GPU devices.
+For GPU device both OpenCL and L0 backends are used.
+
+**NOTE**: The feature isn't supported on FPGA device.
+
+### 1.2. AOT & JIT compilation
+
+All the tests are compiled using AOT, JIT and mixed (AOT with JIT) compilation.
+Mixed compilation is the case when application is built using AOT and used
+shared library uses JIT or vice versa.
+
+### 1.3. Device code split modes
+
+All the tests are compiled using different combination of device code split
+mode.
+There are four possible device code split modes that can be requested via
+`fsycl-device-code-split` compiler's option:
+- `per_kernel` - device code module is created for each SYCL kernel
+- `per_source` - device code module is created for each source
+- `off` - no device code split
+- `auto` - use heuristic to select the best way of splitting device code
+
+For each test the main application and all shared libraries are compiled with
+all the variations of device code split modes. This results in four binaries for
+each application or library.
+Each tests covers all the combinations of device code split modes used for
+the application and libraries, i.e. all binaries of the application are checked
+with all binaries for shared libraries.
+For one application and one shared library examples of the combinations will be:
+- Application compiled with `per_kernel` and library compiled with `per_kernel`
+- Application compiled with `per_kernel` and library compiled with `per_source`
+- Application compiled with `per_kernel` and library compiled with `off`
+- Application compiled with `per_kernel` and library compiled with `auto`
+
+- Application compiled with `per_source` and library compiled with `per_kernel`
+- Application compiled with `per_source` and library compiled with `per_source`
+- Application compiled with `per_source` and library compiled with `off`
+- Application compiled with `per_source` and library compiled with `auto`
+
+and etc. Total 16 combinations.
+
+## 2. Tests
+
+All the tests consist of at least one main application and at least one shared
+library.
+For all the tests simple calculation is performed by the application's kernel(s)
+that used `SYCL_EXTERNAL` from the shared library. Example : addition of
+vectors.
+The result of the calculation must be checked on host.
+
+### 2.1. Basic test with shared library
+
+- Several kernels and `SYCL_EXTERNAL` functions are defined in both library and
+  application.
+- At least one `SYCL_EXTERNAL` function defined in shared library is used from
+  the application's kernel.
+- At least one `SYCL_EXTERNAL` function defined in shared library is used in
+  kernel inside the library.
+- Defined kernels are submitted and ran.
+
+### 2.2. Test with dependent shared libraries
+
+The test consists of the main application and **two** shared libraries libA and
+libB and performs the following:
+- Application defines kernel(s) with dependency on libA.
+- libA defines `SYCL_EXTERNAL` function(s) with dependency on libB.
+- libB defines `SYCL_EXTERNAL` function(s) without external dependencies.
+- Defined kernels are submitted and ran.
+
+### 2.3. Tests with function pointers
+
+#### 2.3.1. Variation 1
+
+- Application defines a function with `indirectly_callable` attribute.
+- Shared library defines host API that can receive function pointer as an
+  argument and runs a kernel that calls through passed function pointer.
+- Address of `indirectly_callable` function is taken and passed to shared
+  library's host API.
+
+#### 2.3.2. Variation 2
+
+- Shared library defines a function with `indirectly_callable` attribute.
+- Shared library defines host API that can return a function pointer to
+  a function with `indirectly_callable` attribute.
+- Application used host API of shared library and calls through received
+  function pointer from a kernel.
+
+### 2.4. Test with shared library without device code
+
+The test aimed to check that support for device code inside shared library
+doesn't break support for host-only shared library.
+
+- Shared library defines host-only non-`SYCL_EXTERNAL` function.
+- The function from shared library is used by host part of the application.
+- Application defines and runs a kernel with a simple calculation.
+
+### 2.5. Tests with run-time loaded shared library
+
+Tests aimed to check that support for dynamic linking of device code doesn't
+break run-time loading of shared library.
+
+#### 2.5.1. Variation 1
+
+The test makes sure that run-time loading of host-only shared libraries is
+not broken.
+
+- Shared library defines several host-only external functions
+- Shared library doesn't contain any device code
+- There is no explicit dependencies between application and library
+- Shared library is loaded via dlopen/LoadLibrary functionality
+- Functions from the shared library are used by host part of the application
+  to perform a simple calculation
+- Result of the simple calculation is checked
+
+#### 2.5.2. Variation 2
+
+The test makes sure that run-time loading of shared libraries with embedded
+device code is not broken.
+
+- Shared library defines several host-only external functions, several
+  `SYCL_EXTERNAL` functions and several kernels
+- There is no explicit dependencies between application and library on
+  device and host
+- Shared library is loaded via dlopen/LoadLibrary functionality
+- Host functions from the shared library are used by host part of the
+  application to perform a simple calculation
+- Result of the simple calculation is checked
+
+### 2.6. Test with two versions of shared library
+
+The test is compiled with version 1 of the shared library and ran with
+shared library of version 2.
+Code can be distributed in the same way as in basic test, but `SYCL_EXTERNAL`
+functions defined in shared library of version 2, should have a different
+definition comparing to version 1, so it is possible to check that correct
+version of the shared library were used.
+
+### 2.7. Test with kernel bundle
+
+The tests aim to check that operations with kernel bundles work correctly in
+co-existence with dynamic linking feature.
+
+#### 2.7.1. Variation 1
+
+- Shared library defines at least one `SYCL_EXTERNAL` function
+- Application defines a kernel with dependency on `SYCL_EXTERNAL` function(s)
+  from the shared library
+- Application gets a `kernel_bundle` object that contains kernel with
+  dependency (can be done via getting `kernel_id` object and using it as a
+  parameter for `get_kernel_bundle` free function overload).
+- Application builds the `kernel_bundle` object and uses it to run the kernel
+  with dependency
+
+#### 2.7.2. Variation 2
+
+- Shared library defines at least one `SYCL_EXTERNAL` function
+- Shared library defines several kernels, at least one kernel from shared
+  library uses `SYCL_EXTERNAL` function
+- Application defines a kernel with dependency on `SYCL_EXTERNAL` function(s)
+  from the shared library
+- Shared library provides a host function that returns `kernel_bundle` object
+  containing kernels from the shared library
+- Application gets a `kernel_bundle` object that contains kernel with
+  dependency and links it using link API with `kernel_bundle` that contains
+  kernels from shared library
+- Resulting `kernel_bundle` object is used to run the kernel with dependency
+  on shared library
+
+### 2.8. Test with several applications
+
+Same as [Basic test with shared library](#Basic-test-with-shared-library) but
+two or more applications using same shared library are ran at the same time.