Adding window_extensions.mk

Adding window_extensions.mk to include all the necessary
packages and properties.

Bug: 235797785
Test: build and verified locally
Change-Id: I79a4152c02d40d6686b98b14c264f3d52c7c4a2c

target/product/window_extensions.mk

@@ -0,0 +1,24 @@
+#
+# Copyright (C) 2022 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+# /system_ext packages
+PRODUCT_PACKAGES += \
+    androidx.window.extensions \
+    androidx.window.sidecar
+
+# properties
+PRODUCT_PRODUCT_PROPERTIES += \
+    persist.wm.extensions.enabled=true