Adds a SPIR-V cache that skips frontend compilation for shaders
that are already compiled in a previous run of Blender.
Initially this was postponed to 4.4 but it was observed that
the vulkan backend didn't perform well on Windows in debug
builds. The reason is that the compiler would also be a debug
build which makes compiling a shader really slow. Starting
Blender on a debug build could take minutes.
So the decision was made to give this task a higher priority so
the vulkan backend would become more usable to developers
as well.
The cache is stored in the application cache dir. The SPIR-V
binaries can be used by different Blender versions so there
is no version specific cache folder.
**Sidecar**: SPIR-V files are a stream of bytes. There is no
header information that allow us to validate the stream. To
add basic validations we could add our custom header or
a sidecar. It was chosen to use a sidecar as having the SPIR-V
files unmodified allows us to load them directly in
debug tools for analyzing.
**Retention**: Shaders that are not used are automatically
removed with a retention period of 30 days.
**Shader builder**: Shader builder cannot use the SPIR-V
cache as it uses stubs that returns invalid cache directories.
This would load/save the cache to the location where you
started the build.
Pull Request: https://projects.blender.org/blender/blender/pulls/128741
3cd579208b