bug#66260: 29.0.92; project.el should support copying a file path relative to the project root

[Juri Linkov]

>> 'C-x p w' does make sense as such, but it would be unfortunate if we
>> find a more important command later which fits the 'w' mnemonics. Maybe
>> 'C-x p W' would be a more conservative choice.
>
> Or even "C-x p C-w".

Or 'C-x p C-c' like 'c' in Info-mode-map for Info-copy-current-node-name.