Add ENABLE_PIP_APP_ICON_OVERLAY experiment

If the flag is on, we apply the app icon over solid color when animating
to PiP if there is no valid source rect hint being provided by the app.

Bug: 265998256
Test: Verify in Flag Flipper
Change-Id: I620b54f723f20bcf23d73d010b9683d8b36acf97

packages/SystemUI/src/com/android/systemui/flags/Flags.kt

@@ -453,6 +453,12 @@ object Flags {
     val ENABLE_PIP_SIZE_LARGE_SCREEN =
         sysPropBooleanFlag(1114, "persist.wm.debug.enable_pip_size_large_screen", default = false)
 
+    // TODO(b/265998256): Tracking bug
+    @Keep
+    @JvmField
+    val ENABLE_PIP_APP_ICON_OVERLAY =
+        sysPropBooleanFlag(1115, "persist.wm.debug.enable_pip_app_icon_overlay", default = false)
+
     // 1200 - predictive back
     @Keep
     @JvmField