Reduce dropped event logging in dispatcher

These logs were guarded with DEBUG_FOCUS until the guard was removed in
this CL:
21431224: Allow new gestures to cancel current gestures

Unfortunately, there's not a good way to reduce these logs. We should
already be logging the decision to drop the initial events like
ACTION_DOWN and ACTION_POINTER_DOWN. So the fact that we are dropping
ACTION_MOVE and others may not be that interesting.

These logs are currently causing people to incorrectly triage bugs to
the input team.

In this CL, make these logs dynamic so that they are only turned on when
needed.

Bug: 245989146
Test: TEST=inputflinger_tests; m $TEST && $ANDROID_HOST_OUT/nativetest64/$TEST/$TEST
Change-Id: I7510fa56d163da1e635b00f4025b3bf2c00ade6e
diff --git a/services/inputflinger/dispatcher/DebugConfig.h b/services/inputflinger/dispatcher/DebugConfig.h
index c7d98ab..c889b9b 100644
--- a/services/inputflinger/dispatcher/DebugConfig.h
+++ b/services/inputflinger/dispatcher/DebugConfig.h
@@ -69,6 +69,16 @@
         android::base::ShouldLog(android::base::LogSeverity::DEBUG, LOG_TAG "Injection");
 
 /**
+ * Generally, we always log whenever events are dropped. However, to reduce logspam, some messages
+ * are suppressed.
+ * Log additional debug messages about dropped input events with this flag.
+ * Enable this via "adb shell setprop log.tag.InputDispatcherDroppedEventsVerbose DEBUG".
+ * Requires system_server restart via `adb shell stop && adb shell start`.
+ */
+const bool DEBUG_DROPPED_EVENTS_VERBOSE =
+        android::base::ShouldLog(android::base::LogSeverity::DEBUG, LOG_TAG "DroppedEventsVerbose");
+
+/**
  * Log debug messages about input focus tracking.
  * Enable this via "adb shell setprop log.tag.InputDispatcherFocus DEBUG" (requires restart)
  */