Warn or delete orphaned extension due to other extension upgrade or uninstall

Real use that happened:

• User installed the Markdown 8.5.4 extension. This installed transitively the "flexmark-ext-ins" extension.
• User then upgraded to Markdown 8.6 extension. The new version of flexmark-java used in 8.6 does not have a dep anymore on "flexmark-ext-ins". Thus this later stayed installed even though it's not orphaned and not used.
• This caused some error during XS upgrade, see https://forum.xwiki.org/t/dashboard-activities-problem-after-12-5-1-1/7160

Ideally the extension should be removed if no other extension is using it and it's been installed as a dep of an extension.