Ignore local transforms when mirroring a partial hierarchy

When mirroring a partial hierarchy remove the local transform
on the mirrored root.  This is necessary because we are placing
the mirrored root under a new parent layer and its original
position relative to the old parent is no longer relevant. This
fixes offsets when mirroring a freeform window.

Flag: com.android.graphics.surfaceflinger.flags.detached_mirror
Fixes: 337845753
Test: atest libsurfaceflinger_unittest
Change-Id: I0453026217f62868a4f6d1362cdc8187baf3f9b0
diff --git a/services/surfaceflinger/FrontEnd/LayerSnapshot.h b/services/surfaceflinger/FrontEnd/LayerSnapshot.h
index 73ee22f..eef8dff 100644
--- a/services/surfaceflinger/FrontEnd/LayerSnapshot.h
+++ b/services/surfaceflinger/FrontEnd/LayerSnapshot.h
@@ -80,6 +80,9 @@
     ui::Transform localTransformInverse;
     gui::WindowInfo inputInfo;
     ui::Transform localTransform;
+    // set to true if this snapshot will ignore local transforms. Used when the snapshot
+    // is a mirror root
+    bool ignoreLocalTransform;
     gui::DropInputMode dropInputMode;
     bool isTrustedOverlay;
     gui::GameMode gameMode;