New rendering backend with support for vulkan, metal

Related: #2852
Also probably depends on #2576 fwiw

Me and @lhog have been discussing this recently. The idea would be to use a nice wrapper over both SDL3_GPU and OpenGL to diversify and abstract our rendering interface. This should increase performance on many platforms and also increase viability on macOS.

This would also prepare Recoil to move away from OpenGL even further, giving games and widgets an alternative interface.

In the short term, due to heavy reliance on raw GL calls by many games, we would need the abstraction to be able to expose the underlying OpenGL context.

Start by reading the related issues #2852 and #2576 to understand the proposed rendering direction and dependencies. Then map where the current rendering interface and raw OpenGL context usage are defined; done would require an agreed abstraction covering SDL3_GPU and OpenGL, with Vulkan and Metal support and compatibility for existing raw GL calls.

Written by the indexing model from the issue text.