Add SDL camera handler

[Megamouse]

• Adds SDL camera handler
• Refactors the bulk of Qt camera handler into a base class shared with SDL camera handler

This can probably be selected to use the PS EYE on windows again. (Didn't test yet).

TODO:

• Check if PS EYE works
• Update settings dialogs

[Megamouse]

I fixed at least one crash. But it can now sometimes softlock. Still needs some more work.

[Darkhost1999]

RPCS3.log

[Kethen]

Thanks for bringing up the concept of main thread of SDL, something I didn't full understand.

Understanding the concept a bit better makes thinking about SDL_PumpEvent() handling a bit weird.

https://github.com/libsdl-org/SDL/blob/2dad6534b841c449100db3a5647fa867ce4db199/include/SDL3/SDL_events.h#L1049-L1071

On one hand, the correct implementation should have both SDL_Init() SDL_PumpEvent() on the same thread, so that it can be a guarantee for some platforms; for instance, window handling on MacOS, and being able to perform callbacks on SDL identified main thread https://github.com/libsdl-org/SDL/blob/2dad6534b841c449100db3a5647fa867ce4db199/src/events/SDL_events.c#L1463

On the other hand, RPCS3 is not currently using SDL window handling and mouse and keyboard input, so just for joystick (maybe even camera) handling, it should be fine as long as SDL_Init() and SDL_PumpEvent() are mutexed; with the current implementation in SDL at least.

I see that the current refactoring ensures that SDL_Init() is done on the qt main thread. Should SDL_PumpEvent() be done on the qt main thread as well for correctness?