Media metadata not being updated when file source field is updated

Media entity has a prepareSave implementation that is tasked with updating media metadata fields if it detects that the source field has changed. The source may have changed in such a way that the media module does not detect.

For a file-based source, it basically just checks that if file id being referenced has changed. But what if the file entity being referenced is the same, but has been updated (like if someone performed a file replacement using the Media Entity File Replace module)? In this case, media does not detect the change and won't update the metadata fields.

There's also no public API to force the regeneration of the metadata fields, but there will be if ✨ Expose triggering update of media metadata + thumbnail to end users Needs work is committed. But even with that issue committed, it may be that we can better detect if a source field has changed.