bug#41633: Prompts incorrect for multi-occur and multi-isearch when using fido-mode

[Juri Linkov <juri@linkov.net>]

> Thanks for the report.  I don't have anything to comment here
> specifically, since I'm not familiar with the modes that you propose
> patching, so let's wait for someone more knowledgeable with those modes.

I don't know who is more knowledgeable since I just blindly
copied that ugly ‘(eq read-buffer-function #'ido-read-buffer)’
from multi-occur to multi-isearch-read-buffers.

Also I see that the patch that Andrew sent works fine in multi-isearch-files.

> However, at first sight, it doesn't seem to be particularly off the
> mark, except that a user might change that binding and break it.  Maybe
> a better, more generic fix would be ask the current minibuffer for the
> answer, perhaps by searching the keymap for the keybinding that maps to
> a command symbol that has a certain property set on it (and then
> fido-mode and ido-mode would play ball).  But maybe that's too
> complex...

Something like this is needed indeed, not too complicated.
If it's not easy to just rephrase the prompt to avoid mentions of
the key, then I suggest to display the string returned from

  (substitute-command-keys "(\\[exit-minibuffer] to end): ")

called in the minibuffer.