Disallow system apps to be installed/updated as instant.

Bug: 299441833
Test: atest android.content.pm.cts.PackageManagerTest
Change-Id: Idd89a6dd72f0e68259095f677185f0494391025c
diff --git a/services/core/java/com/android/server/pm/InstallPackageHelper.java b/services/core/java/com/android/server/pm/InstallPackageHelper.java
index 65bfb2f..985dadf 100644
--- a/services/core/java/com/android/server/pm/InstallPackageHelper.java
+++ b/services/core/java/com/android/server/pm/InstallPackageHelper.java
@@ -672,6 +672,9 @@
                 if (pkgSetting == null || pkgSetting.getPkg() == null) {
                     return Pair.create(PackageManager.INSTALL_FAILED_INVALID_URI, intentSender);
                 }
+                if (instantApp && (pkgSetting.isSystem() || pkgSetting.isUpdatedSystemApp())) {
+                    return Pair.create(PackageManager.INSTALL_FAILED_INVALID_URI, intentSender);
+                }
                 if (!snapshot.canViewInstantApps(callingUid, UserHandle.getUserId(callingUid))) {
                     // only allow the existing package to be used if it's installed as a full
                     // application for at least one user