shader: Move pipeline cache logic to separate files

Move code to separate files to be able to reuse it from OpenGL. This
greatly simplifies the pipeline cache logic on Vulkan.

Transform feedback state is not yet abstracted and it's still
intrusively stored inside vk_pipeline_cache. It will be moved when
needed on OpenGL.

src/video_core/CMakeLists.txt

@@ -145,7 +145,10 @@ add_library(video_core STATIC
     renderer_vulkan/vk_texture_cache.h
     renderer_vulkan/vk_update_descriptor.cpp
     renderer_vulkan/vk_update_descriptor.h
+    shader_cache.cpp
     shader_cache.h
+    shader_environment.cpp
+    shader_environment.h
     shader_notify.cpp
     shader_notify.h
     surface.cpp