Expose SDL_Gamepad* handle via PAD API

[PJB3005]

Will be using this in Dusk for input mapping etc

[Antidote]

I don't think this is a good idea, if you need more mapping functionality please create new PAD APIs, don't expose the underlying handle.

[encounter]

I looked over the associated PR and it's fine. We could probably expose SDL_GetGamepadType and SDL_GetGamepadButtonLabel via PAD API, but at the same time, I agree with the argument that we should allow using SDL APIs directly. We already do this for windowing (we hand the caller the SDL_Window* in AuroraInfo), so getting the SDL_Gamepad* handle also seems reasonable.

Yes, we should be careful to limit how much we rely on the underlying handles, and add Aurora APIs where it makes sense to, but we should not strive to reinvent the SDL API surface.