Currently assumes a single gamepad, has no code specific to gamepad
detection (gamepad is "detected" when an event related to gamepad
arrives). Also assumes that all gamepads look roughly like an xbox/ps
controller. Both assumptions are not strictly true, but an
implementation like that probably covers 85% of usecases.
Also it doesn't update previousButtonState so functions
IsGamepadButtonPressed() and IsGamepadButtonReleased() don't work, but
they didn't work previously on Android anyway, and they are flaky on
desktop as they are now, so the mechanism for these two functions
probably should be reworked anyway.
It's certainly an improvement compared to the previous android gamepad
handling code, which put gamepad events into touch related structs.
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