Add flicker test for ActivityEmbedding (1/n)

Add base and helper classes for ActivityEmbedding flicker tests.

Bug: 238043427
Test: atest FlickerTests:OpenActivityEmbeddingPlaceholderSplit
Change-Id: I60dae000fbb22e70aebea1f7c42ddce490c10bab
diff --git a/tests/FlickerTests/Android.bp b/tests/FlickerTests/Android.bp
index 7731e09..855d3c1 100644
--- a/tests/FlickerTests/Android.bp
+++ b/tests/FlickerTests/Android.bp
@@ -46,6 +46,7 @@
         "launcher-helper-lib",
         "launcher-aosp-tapl",
         "platform-test-annotations",
+        "wm-flicker-window-extensions",
     ],
 }
 
@@ -83,5 +84,21 @@
         "flickertestapplib",
         "truth-prebuilt",
         "app-helpers-core",
+        "wm-flicker-window-extensions",
     ],
 }
+
+android_library_import {
+    name: "wm-flicker-window-extensions_nodeps",
+    aars: ["libs/window-extensions-release.aar"],
+    sdk_version: "current",
+}
+
+java_library {
+    name: "wm-flicker-window-extensions",
+    sdk_version: "current",
+    static_libs: [
+        "wm-flicker-window-extensions_nodeps",
+    ],
+    installable: false,
+}