Refactor syncing between communal STL state and KTF

This introduces a new CommunalSceneTransitionInteractor which handles
syncing between the two state machines.

Similarly, it introduces new APIs for callers to set the desired KTF
state when changing scenes programatically.

Bug: 327225415
Test: atest CommunalSceneTransitionInteractorTest
Flag: com.android.systemui.communal_scene_ktf_refactor
Change-Id: If5a6165713a2933be92730bcb8321393700e0ba1
diff --git a/packages/SystemUI/aconfig/systemui.aconfig b/packages/SystemUI/aconfig/systemui.aconfig
index 71f5511..062a19a 100644
--- a/packages/SystemUI/aconfig/systemui.aconfig
+++ b/packages/SystemUI/aconfig/systemui.aconfig
@@ -981,6 +981,16 @@
 }
 
 flag {
+  name: "communal_scene_ktf_refactor"
+  namespace: "systemui"
+  description: "refactors the syncing mechanism between communal STL and KTF state."
+  bug: "327225415"
+  metadata {
+    purpose: PURPOSE_BUGFIX
+  }
+}
+
+flag {
   name: "app_clips_backlinks"
   namespace: "systemui"
   description: "Enables Backlinks improvement feature in App Clips"