SF: omit vsync callbacks when screen is OFF

This CL is submitted behind a flag and in still in development.
The flag should not be enabled just yet.

Test: manual
Bug: 331636736
Flag: com.android.graphics.surfaceflinger.flags.no_vsyncs_on_screen_off
Change-Id: Iec9cde3bafb9c112c9ce9beebe6dded4727fc99c
diff --git a/services/surfaceflinger/DisplayDevice.cpp b/services/surfaceflinger/DisplayDevice.cpp
index 402a3d2..c743ea2 100644
--- a/services/surfaceflinger/DisplayDevice.cpp
+++ b/services/surfaceflinger/DisplayDevice.cpp
@@ -201,6 +201,10 @@
     return mPowerMode != hal::PowerMode::OFF;
 }
 
+bool DisplayDevice::isRefreshable() const {
+    return mPowerMode == hal::PowerMode::DOZE || mPowerMode == hal::PowerMode::ON;
+}
+
 ui::Dataspace DisplayDevice::getCompositionDataSpace() const {
     return mCompositionDisplay->getState().dataspace;
 }