miatoll: Import Keyhandler from Davinci

https://github.com/ArianK16a/android_device_xiaomi_davinci

This tells Inputdispatcher to ignore inputs from our Fingerprint scanner, as that seems to be causing ANRs

keyhandler/proguard.flags

@@ -0,0 +1,4 @@
+# Keep keyhandler constructor
+-keep public class * implements com.android.internal.os.DeviceKeyHandler {
+    public <init>(android.content.Context);
+}