Ei protocol support

- Use the configured keyboard layout, track ei seats to reconfigure their keyboards
- DBus interface
- Disambiguate input devices per backend instance
- Add support for `ei_keysym` and `ei_text`
- Act as input method for ei_text UTF-8 injection
- Create a region per output for abosolute pointer position
- Map ei region for touchscreen emulation
- Release pointer buttons and keys on removal
- Send modifiers to EI connections

src/backend/kms/mod.rs

@@ -211,7 +211,7 @@ fn init_libinput(
             state.backend.kms().input_devices.remove(&*device.name());
         }
 
-        state.process_input_event(event);
+        state.process_input_event(event, crate::input::InputBackendId::Normal);
 
         for output in state.common.shell.read().outputs() {
             state.backend.kms().schedule_render(output);