surfaceflinger: put RefreshRateOverlay in the center for circular displays

- Use debug.sf.show_refresh_rate_overlay_in_middle sysprop to turn on.

Test: Visual
Before: screenshot/3nJHsbGsXAjLWNr
After: screenshot/3RtYGnCAe5M2Pf9

Bug: 265356373
Change-Id: Ib598e6f5c7a1c4b13fa4d6e4dbc2e29b2e25bfc8
diff --git a/services/surfaceflinger/RefreshRateOverlay.h b/services/surfaceflinger/RefreshRateOverlay.h
index d6f828f..b68a88c 100644
--- a/services/surfaceflinger/RefreshRateOverlay.h
+++ b/services/surfaceflinger/RefreshRateOverlay.h
@@ -54,6 +54,7 @@
     enum class Features {
         Spinner = 1 << 0,
         RenderRate = 1 << 1,
+        ShowInMiddle = 1 << 2,
     };
 
     RefreshRateOverlay(FpsRange, ftl::Flags<Features>);