gl/vk/rsx: Refactoring; unify texture cache code
gl: Fixups
- Removes rsx::gl::texture class and leave gl::texture intact
- Simplify texture create and upload mechanisms
- Re-enable texture uploads with the new texture cache mechanism
rsx: texture cache - check if bit region fits into dst texture before attempting to copy
gl/vk: Cleanup
- Set initial texture layout to DST_OPTIMAL since it has no data in it anyway at the start
- Move structs outside of classes to avoid clutter
