* renderer_opengl: Namespace OpenGL code
Namespaces all OpenGL code under the OpenGL namespace.
Prevents polluting the global namespace and allows clear distinction
between other renderers' code in the future.
* Also namespace TextureCubeConfig
In a future commit, the count of cached pages will be reintroduced in
the actual surface cache. Also adds an Invalidate only to the cache
which marks a region as invalid in order to try to avoid a costly flush
from 3ds memory
This removes explicit checks sprinkled all over the codebase to instead
just have the SW rasterizer expose an implementation with no-ops for
most operations.
