Make WallpaperMS bind wallpaper component PendingIntent immutable.

Require that the PendingIntent be immutable so that a malicious app is
not able to hijack and mutate any of the details.

Fixes: 154915372
Test: build & flash, change wallpaper manually.
Change-Id: I59b48811b26736bf0575769107dd940ca33ccf8d
(cherry picked from commit d4bd69cef0)

services/core/java/com/android/server/wallpaper/WallpaperManagerService.java

@@ -2133,7 +2133,7 @@ public class WallpaperManagerService extends IWallpaperManager.Stub {
                     mContext, 0,
                     Intent.createChooser(new Intent(Intent.ACTION_SET_WALLPAPER),
                             mContext.getText(com.android.internal.R.string.chooser_wallpaper)),
-                    0, null, new UserHandle(serviceUserId)));
+                    PendingIntent.FLAG_IMMUTABLE, null, new UserHandle(serviceUserId)));
             if (!mContext.bindServiceAsUser(intent, newConn,
                     Context.BIND_AUTO_CREATE | Context.BIND_SHOWING_UI
                             | Context.BIND_FOREGROUND_SERVICE_WHILE_AWAKE,