Add clear command to `watch` command

This CL adds a `clear` command to CameraServer's watch command to clear
any cached dumps from watched clients.

Bug: 199746421
Test: Manually Tested
Change-Id: I2d8092ab2a88a5ac838e8def0685543b46362752
diff --git a/services/camera/libcameraservice/CameraService.h b/services/camera/libcameraservice/CameraService.h
index cb26763..4bbfc7b 100644
--- a/services/camera/libcameraservice/CameraService.h
+++ b/services/camera/libcameraservice/CameraService.h
@@ -1180,6 +1180,9 @@
     // Disable tag monitoring
     status_t stopWatchingTags(int outFd);
 
+    // Clears mWatchedClientsDumpCache
+    status_t clearCachedMonitoredTagDumps(int outFd);
+
     // Print events of monitored tags in all cached and attached clients
     status_t printWatchedTags(const Vector<String16> &args, int outFd);