Now that the GPU is initialized when video backends are initialized,
it's no longer needed to query components once the game is running: it
can be done when yuzu is booting.
This allows us to pass components between constructors and in the
process remove all Core::System references in the video backend.
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.