Move reference WM Sidecar impl to system_ext

Placing the reference implementation in /vendor partition tirggers
UnofficialApisUsageTest failures due to hidden API use in the sample.
Moving it to system_ext should resolve this issue.

Bug: 167214265
Test: com.android.gts.api.UnofficialApisUsageTest#testNonApiReferences
Change-Id: I628fd0e00558208a3af26ecf02b82a3cedad8011
(cherry picked from commit 4ebadc8056)

libs/WindowManager/Jetpack/Android.bp

@@ -24,14 +24,14 @@ java_library {
     static_libs: ["window-sidecar"],
     installable: true,
     sdk_version: "core_platform",
-    vendor: true,
+    system_ext_specific: true,
     libs: ["framework", "androidx.annotation_annotation",],
     required: ["androidx.window.sidecar.xml",],
 }
 
 prebuilt_etc {
     name: "androidx.window.sidecar.xml",
-    vendor: true,
+    system_ext_specific: true,
     sub_dir: "permissions",
     src: "androidx.window.sidecar.xml",
     filename_from_src: true,

libs/WindowManager/Jetpack/androidx.window.sidecar.xml

@@ -17,5 +17,5 @@
 <permissions>
     <library
         name="androidx.window.sidecar"
-        file="/vendor/framework/androidx.window.sidecar.jar"/>
+        file="/system_ext/framework/androidx.window.sidecar.jar"/>
 </permissions>