Use enum class for DropReason

Using enum class provides type safety and helps ensure there are no
missed switch/case statements at compile time.

Bug: 70668286
Test: presubmit
Change-Id: Ia3d761d2aec0694edcf8ce24643f17e25cd79a1b
diff --git a/services/inputflinger/dispatcher/InputDispatcher.h b/services/inputflinger/dispatcher/InputDispatcher.h
index 1f906e4..9d22e2c 100644
--- a/services/inputflinger/dispatcher/InputDispatcher.h
+++ b/services/inputflinger/dispatcher/InputDispatcher.h
@@ -113,14 +113,13 @@
     virtual status_t pilferPointers(const sp<IBinder>& token) override;
 
 private:
-
-    enum DropReason {
-        DROP_REASON_NOT_DROPPED = 0,
-        DROP_REASON_POLICY = 1,
-        DROP_REASON_APP_SWITCH = 2,
-        DROP_REASON_DISABLED = 3,
-        DROP_REASON_BLOCKED = 4,
-        DROP_REASON_STALE = 5,
+    enum class DropReason {
+        NOT_DROPPED,
+        POLICY,
+        APP_SWITCH,
+        DISABLED,
+        BLOCKED,
+        STALE,
     };
 
     sp<InputDispatcherPolicyInterface> mPolicy;