[SYCL] Refactor program to improve ABI stability

[alexbatashev]

This patch is a part of effort to decouple SYCL Runtime library
interface from its actual implementation. The goal is to improve
SYCL ABI/API compatibility between different versions of library.

The following modifications were applied to program and program_impl
classes:

1. Removed include of program_impl header from program.hpp and replaced
   it with forward declaration.
2. Move member function implementations from program.hpp to program.cpp
3. std::shared_ptr was replaced with shared_ptr_class for program class
4. Documentation was improved for both program and program_impl
5. program_impl now tries to follow LLVM code style
6. program_impl now uses string kernel name instead of kernel type

Applying aforementioned changes requires modifying other header files.
While some of those may seem as a regression, affected classes will be
covered by future patches.

Signed-off-by: Alexander Batashev [email protected]

[AlexeySachkov]

shared_ptr_class?

[keryell]

All these _class will probably be deprecated at some point, so I do not thing this change is important.

[alexbatashev]

@AlexeySachkov although it is not part of public interface and these methods are not called outside RT (thus no need to use _class), I still applied your suggestion as it makes call stack more consistent (less conversion between different types).

@keryell that's new information for me. Is there some discussion or any other source of information so I can ramp up myself?

[keryell]

Talk to your SYCL committee representative. I think the problem is that it is not really implementable in a portable way and not testable with some CTS... So why not just using the STL nowadays?

[alexbatashev]

@romanovvlad ping