Hide system apps until installed (1/2)

Applying this mechanism for system carrier apps to make visibility
reasonable from the user's perspective. In other words, before
hidden system apps have been installed, they wouldn't be listed
via APIs in PackageManager which are used at all apps list and
search in Settings and so on.

Test: manual
Test: atest CarrierAppUtilsTest
Test: atest PackageManagerTest
Bug: 74068582
Change-Id: Id3ff138ad529b909d9bbf6719af3a553b909ccbb
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index e35b631..19e5e21 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -3024,6 +3024,15 @@
     <permission android:name="android.permission.INSTALL_PACKAGE_UPDATES"
         android:protectionLevel="signature|privileged" />
 
+    <!-- Allows an application to install existing system packages. This is a limited
+         version of {@link android.Manifest.permission#INSTALL_PACKAGES}.
+         <p>Not for use by third-party applications.
+         TODO(b/80204953): remove this permission once we have a long-term solution.
+         @hide
+    -->
+    <permission android:name="com.android.permission.INSTALL_EXISTING_PACKAGES"
+        android:protectionLevel="signature|privileged" />
+
     <!-- @SystemApi Allows an application to clear user data.
          <p>Not for use by third-party applications
          @hide