bug#43153: Add new command project-find-dir (and move binding of project-dired)

[Stefan Kangas]

Juri Linkov <juri@linkov.net> writes:

> Maybe then better to rename `project-dired' to `project-root-dired',
> then bind `C-x p D' to `project-root-dired' without the prompt,
> and bind `project-dired' to `C-x p d' with a prompt that
> asks for a directory like `C-x p f' (project-find-file).

Agreed.  Let's see what Dmitry thinks about it.