video_core: Implement API agnostic view based texture cache

Implements an API agnostic texture view based texture cache. Classes
defined here are intended to be inherited by the API implementation and
used in API-specific code.

This implementation exposes protected virtual functions to be called
from the implementer.

Before executing any surface copies methods (defined in API-specific code)
it tries to detect if the overlapping surface is a superset and if it
is, it creates a view. Views are references of a subset of a surface, it
can be a superset view (the same as referencing the whole texture).
Current code manages 1D, 1D array, 2D, 2D array, cube maps and cube map
arrays with layer and mipmap level views. Texture 3D slices views are
not implemented.

If the view attempt fails, the fast path is invoked with the overlapping
textures (defined in the implementer). If that one fails (returning
nullptr) it will flush and reload the texture.

src/video_core/CMakeLists.txt

@@ -106,6 +106,8 @@ add_library(video_core STATIC
     textures/decoders.cpp
     textures/decoders.h
     textures/texture.h
+    texture_cache.cpp
+    texture_cache.h
     video_core.cpp
     video_core.h
 )