Reduces some header churn and reduces rebuilds when some header
internals change.
While we're at it we can also resolve a missing include in buffer_cache.
Deduplicate code shared between vk_pipeline_cache and gl_shader_cache as
well as shader decoder code.
While we are at it, fix a bug in gl_shader_cache where compute shaders
had an start offset of a stage shader.
The intention behind this was to assign a float to from an uint32_t, but
it was unintentionally being copied directly into the std::optional.
Copy to a temporary and assign that temporary to std::optional. This can
be replaced with std::bit_cast<float> once we are in C++20.
Implement accessing textures through an index. It uses the same
interface as OpenGL, the main difference is that Vulkan bindings are
forced to be arrayed (the binding index doesn't change for stacked
textures in SPIR-V).
Some games like The Legend of Zelda: Breath of the Wild assign
render targets without writing them from the fragment shader. This
generates Vulkan validation errors, so silence these I previously
introduced a commit to set "vec4(0, 0, 0, 1)" for these attachments. The
problem is that this is not what games expect. This commit reverts that
change.