Move FlagManager to a common SF lib

So that CompositionEngine can use it.

Bug: 236745178
Test: builds
Change-Id: Ib873cb4a0b4231723a22fbc8fa22ec955aa6f329
diff --git a/services/surfaceflinger/Scheduler/EventThread.cpp b/services/surfaceflinger/Scheduler/EventThread.cpp
index 7f627f8..693a357 100644
--- a/services/surfaceflinger/Scheduler/EventThread.cpp
+++ b/services/surfaceflinger/Scheduler/EventThread.cpp
@@ -43,9 +43,9 @@
 #include <utils/Errors.h>
 #include <utils/Trace.h>
 
+#include <common/FlagManager.h>
 #include <scheduler/VsyncConfig.h>
 #include "DisplayHardware/DisplayMode.h"
-#include "FlagManager.h"
 #include "FrameTimeline.h"
 #include "VSyncDispatch.h"
 #include "VSyncTracker.h"