Support unowned SDL_GPUDevice handles

[pixlark]

SDL_GPUDevice isn't always instantiated by rust usercode. In the case where you need to access the GPU Device that's initialized by the 2D renderer, you can get a *mut SDL_GPUDevice handle, but you can't turn that into a Device.
Here is an official SDL example demonstrating how this would be done in C.

The examples goes through a few hoops in order to get the GPUDevice pointer, namely reading it from a pointer property on the SDL_Renderer - so because of that, maybe this wouldn't be considered a primary enough usecase to warrant being supported by the Rust API.

However, in SDL 3.4, there will be a new function SDL_CreateGPURenderer, which removes those hoops and provides you with an SDL_GPUDevice pointer that is owned by the SDL_Renderer. So when 3.4 comes out, this problem will need to be dealt with anyways.

Internally, the SDL_GPUDevice pointer in a Device is held by DeviceContainer, which assumes ownership over the pointer, meaning that when it's dropped, it callsSDL_DestroyGPUDevice.

This means that you can't just add an unsafe fn from_pointer(ptr: *mut SDL_GPUDevice) -> Device without running into double-free issues (in my experience it caused a hard crash when trying to close the program).

So in order to support an unowned Device, the type would need to be refactored somehow, perhaps by creating another DeviceRef<'a> type that borrows from an owned Device, and using that everywhere instead? Similar to String vs. &str?

I'm not really sure, which is why I'm creating this issue instead of just submitting a PR - hopefully someone more familiar with these bindings has some ideas. I am open to doing the legwork though and writing the PR, just not sure how to go about it.