Fix Updater PHPStan L0 issues

+++ b/core/lib/Drupal/Core/Updater/Updater.php
@@ -194,6 +194,23 @@ public static function getProjectTitle($directory) {
+  public function getInstallDirectory() {
+    throw new \BadMethodCallException(get_class() . '::getInstallDirectory() not implemented.');

I am sure in this case this could just be abstract? Updaters are only used by core, there are only Module and Theme implementations, and I don't see a use case outside of that.

Thanks, I think this is fine even if it's technically an API change - all this Updater code should be considered internal as far as I can see.

Committed d96c99b and pushed to 10.1.x. Thanks!
Committed 104a255 and pushed to 10.0.x. Thanks!

I debated whether we should have a CR for this but I don't think so. The only stuff I can find in contrib is from clones of core... see https://git.drupalcode.org/search?group_id=2&page=3&repository_ref=&scop...

I think we should file a follow-up for the abstract class to implement \Drupal\Core\Updater\UpdaterInterface and then fix the docs in the abstract to use @inheritdoc.