Convert input event type to enum class

This will increase type safety and simplify some of the printing.

Bug: 274073185
Test: m checkinput
Change-Id: I848c2f156cc23232c50d2338b4788be3232dba1a
diff --git a/libs/input/android/os/InputEventInjectionSync.aidl b/libs/input/android/os/InputEventInjectionSync.aidl
index 95d24cb..2d225fa 100644
--- a/libs/input/android/os/InputEventInjectionSync.aidl
+++ b/libs/input/android/os/InputEventInjectionSync.aidl
@@ -33,4 +33,7 @@
 
     /* Waits for the input event to be completely processed. */
     WAIT_FOR_FINISHED = 2,
+
+    ftl_first = NONE,
+    ftl_last = WAIT_FOR_FINISHED,
 }