DEV: Function to get baseUri from get-url helper (PR #10444)

This is a useful variable to have


Why do you need this though? So far other code has avoided it so I am curious.

@eviltrout This returns just the subfolder path, if one is present. It is useful to me in my Plugin Adventures :tm:, and seems generally useful. Not sure a cleaner way to get just the subfolder path otherwise!

You can call get-url "/" right?

@eviltrout :facepalm: