Vk Pixel History: MSAA depth/stencil copy, shader out

Use a separate compute shader module for MSAA copy, and output
directly into the destination buffer instead of creating
staging resources.

Support case where there is no depth stencil attachment to get post mod
values in per fragment reporting. Previously used the original
framebuffer that might not have had depth/stencil view, so couldn't
count the fragments. Now use the sub image.

To get the post mod color, we need to blend with the premod color, so
we use vkCmdCopyImage to copy from the original image.

renderdoc/driver/vulkan/vk_shader_cache.cpp

@@ -91,6 +91,8 @@ static const BuiltinShaderConfig builtinShaders[] = {
      rdcspv::ShaderStage::Fragment, FeatureCheck::NoCheck, true},
     {BuiltinShader::TexRemapSInt, EmbeddedResource(glsl_texremap_frag),
      rdcspv::ShaderStage::Fragment, FeatureCheck::NoCheck, true},
+    {BuiltinShader::PixelHistoryMSCopyCS, EmbeddedResource(glsl_pixelhistory_mscopy_comp),
+     rdcspv::ShaderStage::Compute, FeatureCheck::NoCheck, true},
     {BuiltinShader::PixelHistoryPrimIDFS, EmbeddedResource(glsl_pixelhistory_primid_frag),
      rdcspv::ShaderStage::Fragment, FeatureCheck::NoCheck, true},
     {BuiltinShader::ShaderDebugSampleVS, EmbeddedResource(glsl_shaderdebug_sample_vert),