Merge: gamnit: use SDL2 windows and events

_gamnit_ update to use SDL2 instead of SDL1.2. This change brings better code portability and fixes a few known SDL1.2 limitations. This PR does not significantly change the API, asides from removing the workarounds for old limitations.

As support, this PR also:
* Adds more SDL2 events and surface services.
* Updates the `opengles1_hello_triangle` example to use SDL2 and make it compatible with ANGLE and Windows.
* Drops the _gamnit_ workarounds for the previously slow mouse move events and mouse wrap for FPS like controls.
* Fixes shader compatibility with some graphics card and driver.
* General cleanup for the `egl` module.

Pull-Request: #2376
Reviewed-by: Jean Privat <jean@pryen.org>