Copy RequestedUpdateValidator to automatic_updates_extensions

Not a lot of complaints here. I'm not a huge fan of the way the validator itself is written, but it's also a direct copy from Automatic Updates so it's out of scope here.

@phenaproxima re

how do we account for dependencies being updated?

This validator is not concern with dependencies being updated. It only deals with the packages that directly request to be updated. This validator like the one in automatic_updates are really just fail safe in the case that Composer operation succeeded but for some reason the directly requested projects were not updated we should fail.

I added updates to other packages in the test to prove these are allowed.

Okay, that explanation makes sense to me.

Automatically closed - issue fixed for 2 weeks with no activity.