Thanks. Here is the updated patch. I tested it with minibuffer-only
frames, and it seems to work.
Are you sure that it's okay to rebind M-c in
minibuffer-local-completion-map? It's a good mnemonic for
"completion", but it hides the capitalize-word binding, that users
might possibly want to use there (I don't, it's only when thinking
about this patch that I realized this).
Another option would be M-g, which would not hide anything that is
possibly useful in the minibuffer, and is still a mnemonic of "goto".
Thanks; applied to Emacs 28.
I went with `M-g' -- it seems pretty natural here. If anybody else
wants a different key binding, go ahead and change it.