KeyHandler: Integrate in tri-state-key handling via UEventObserver API

This basically adds required code to support both switch and extcon
based tri-state-key. This also adds tri-state-key-calibrate script for
devices that need to be calibrated on boot (OnePlus7+)

Change-Id: I2e6c5d2861569750bead05edacf6e328a5227077

KeyHandler/Android.bp

@@ -17,3 +17,10 @@ android_app {
         proguard_flags_files: ["proguard.flags"],
     },
 }
+
+sh_binary {
+    name: "tri-state-key-calibrate",
+    init_rc: ["tri-state-key-calibrate.rc"],
+    src: "tri-state-key-calibrate.sh",
+    vendor: true,
+}