Touch input for SDL2

[nkast]

This implements Touch input for the SDL2 backend.

In order to prevent Touches to appear as Mouse input, we now use SDL_GetMouseState instead of https://wiki.libsdl.org/SDL2/SDL_GetGlobalMouseState, which change the behavior of Mouse.GetState().

• Mouse input doesn't escape the Window bounds. This makes windowed mode behave more like a fullscreen mode. This is also how touch input is implemented in this PR and on the WinForms backend. Touch outside the window are released.
• We lost the ability to query up to date mouse position, because GetMouseState is updated during the event pump.
• docs report that GetGlobalMouseState was less efficient.
• The change could fix a reported bug on linux/hyprland.

related to #2619
closes #2603
resolves #2562

[squarebananas]

Mouse input doesn't escape the Window bounds.

That differs quite differently in behavior compared to other platforms. Wouldn't that mean in windowed mode:

• Custom game cursors get stuck on the window edge rather than leave the window as expected.
• 3d camera controls where you drag the mouse to move the camera around would seem glitchy if the mouse leaves the window.
• If the user places a custom scroll bar against a side of a window edge, momentarily moving slightly outside the window while dragging the scroll element would stop input updates occurring.