rasterizer_accelerated: Add intermediary for GPU rasterizers

Add an intermediary class that implements common functions across GPU
accelerated rasterizers. This avoids code repetition on different
backends.

src/video_core/CMakeLists.txt

@@ -36,6 +36,8 @@ add_library(video_core STATIC
     memory_manager.h
     morton.cpp
     morton.h
+    rasterizer_accelerated.cpp
+    rasterizer_accelerated.h
     rasterizer_cache.cpp
     rasterizer_cache.h
     rasterizer_interface.h