This fixes:
- menu toggle erratically not working on Android
- stray input going to libretro core when resuming content
- bound keys triggering as soon as they're bound on Android
- menu key repeat also repeating keys which should not be repeated
- issues caused by relying on timeouts for flushing
Architectural changes:
- menu_ctx_driver_t::input_postprocess now takes state and old_state
(this allows getting rid of menu_handle_t::trigger_state)
Related changes:
- remove some no-op input_postprocess handlers (same effect as NULL)
- menu_iterate now uses the parameters passed to it, instead of
polling menu_input
- menu_input is now merged into meta_input_keys_pressed
