Fix OpImageRead result type when compiling HLSL
- Per the Vulkan spec, OpImageRead must return a 4-component vector always. When compiling HLSL, loads from a RWTexture of a template type with < 4 components would incorrectly generate an OpImageRead with a < 4 component result, resulting in validation errors.
- This was previously fixed for OpImageFetch in commit 4425f24; this commit does the same thing for OpImageRead.
- Added associated tests and expanded existing image fetch tests to check all the different types of textures, in both float and int incarnations, for completeness.
- Update other HLSL tests involving OpImageRead
HLSL allows image and texture types to be templatized on sub-vec4 types,
or even structures. This was mostly handled already during creation of
sampling operations. However, for operator[] which can generate image
loads, this wasn't happening.
It also isn't very easy to do at that point in time, because operator[]
does not know where the results it produces will end up. They may be
an lvalue or an rvalue, and there's a post-process to convert loads to
stores. They may end up in atomic ops.
To bypass that difficulty, GlslangToSpv now looks for this case and
adds the appropriate conversion. LIMITATION: this only works for
cases for which a simple conversion opcode suffices. That is to say,
it will not work if the type is templatized on a struct.
