Add keyboard overlay preset, keyboard submenu, and osk_toggle hotkey. Use overlay caching for osk_toggle.
For now, keyboard menu has only preset path, auto-scale toggle, and opacity.
Related fixes:
- input_keyboard_event: Don't check hotkey binds when device is RETRO_DEVICE_POINTER
- Add input_keymaps_translate_rk_to_ascii() for correct character input to input_keyboard_event
- input_overlay_poll: Delay clearing INPUT_OVERLAY_BLOCKED flag until there is no overlay input (Avoids stray input after osk_toggle)
- Send keyboard events for modifiers before other keys (for correct modifier+key input if hitboxes overlap)