[SYCL][NFC] Add initializers to local variables (#7350)

This patch aims to improve situation with unit-tests: a lot of PI
routines only have dummy mock versions of them. Dummy mocks ignore all
arguments, leaving out-parameters untouched. Depending on how they used
at call site, this could lead to some obscure errors like `bad_alloc` if
an uninitialized value was used to set a size of a `vector`.

Discovered while working on a unit-test in #7333

Author: AlexeySachkov

sycl/source/detail/kernel_info.hpp

@@ -47,7 +47,7 @@ template <typename Param>
 typename std::enable_if<
     std::is_same<typename Param::return_type, uint32_t>::value, uint32_t>::type
 get_kernel_info(RT::PiKernel Kernel, const plugin &Plugin) {
-  uint32_t Result;
+  uint32_t Result = 0;
 
   // TODO catch an exception and put it to list of asynchronous exceptions
   Plugin.call<PiApiKind::piKernelGetInfo>(Kernel, PiInfoCode<Param>::value,
@@ -83,7 +83,7 @@ get_kernel_device_specific_info(RT::PiKernel Kernel, RT::PiDevice Device,
                                 const plugin &Plugin) {
   static_assert(is_kernel_device_specific_info_desc<Param>::value,
                 "Unexpected kernel_device_specific information descriptor");
-  typename Param::return_type Result;
+  typename Param::return_type Result = {};
   // TODO catch an exception and put it to list of asynchronous exceptions
   get_kernel_device_specific_info_helper<Param>(
       Kernel, Device, Plugin, &Result, sizeof(typename Param::return_type));
@@ -98,7 +98,7 @@ get_kernel_device_specific_info(RT::PiKernel Kernel, RT::PiDevice Device,
                                 const plugin &Plugin) {
   static_assert(is_kernel_device_specific_info_desc<Param>::value,
                 "Unexpected kernel_device_specific information descriptor");
-  size_t Result[3];
+  size_t Result[3] = {0, 0, 0};
   // TODO catch an exception and put it to list of asynchronous exceptions
   get_kernel_device_specific_info_helper<Param>(Kernel, Device, Plugin, Result,
                                                 sizeof(size_t) * 3);
@@ -121,7 +121,7 @@ uint32_t get_kernel_device_specific_info_with_input(RT::PiKernel Kernel,
                 "Unexpected kernel_device_specific information descriptor for "
                 "query with input");
   size_t Input[3] = {In[0], In[1], In[2]};
-  uint32_t Result;
+  uint32_t Result = 0;
   // TODO catch an exception and put it to list of asynchronous exceptions
   Plugin.call<PiApiKind::piKernelGetSubGroupInfo>(
       Kernel, Device, PiInfoCode<Param>::value, sizeof(size_t) * 3, Input,