Add an action to copy CWD path to clipboard

I think this is pretty self explanatory.
Similar concerns as the "Open in File Explorer" action, #12859.
Maybe there's a way to make the action do nothing if the active Terminal hasn't set one?

Also relevant: #3337, #5916

Start by reading the existing "Open in File Explorer" action in issue #12859 and the related issues #3337 and #5916. Trace how actions access the active Terminal's current working directory; done means a new action copies that path to the clipboard and safely does nothing when no path is set.

Written by the indexing model from the issue text.