[1/n] Create Flag for Compat UI Framework

Creates the flag for the compat ui framework implementation.

Flag: com.android.window.flags.app_compat_ui_framework
Fix: 304234563
Bug: 270361630
Test: m

Change-Id: If2d951557b5ebe03f251887a1252a37c162a40a3
diff --git a/core/java/android/window/flags/large_screen_experiences_app_compat.aconfig b/core/java/android/window/flags/large_screen_experiences_app_compat.aconfig
index 5b99ff9..cc880e1 100644
--- a/core/java/android/window/flags/large_screen_experiences_app_compat.aconfig
+++ b/core/java/android/window/flags/large_screen_experiences_app_compat.aconfig
@@ -113,4 +113,12 @@
     namespace: "large_screen_experiences_app_compat"
     description: "Enables sysui animation for user aspect ratio button"
     bug: "300357441"
+}
+
+flag {
+  name: "app_compat_ui_framework"
+  namespace: "large_screen_experiences_app_compat"
+  description: "Whether the declarative compat UI framework is enabled"
+  bug: "270361630"
+  is_fixed_read_only: true
 }
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