bug#15200: isearch-other-meta-char and shift

[Juri Linkov]

>> IIUC, the biggest challenge is to add a new argument
>> to set-temporary-overlay-map that will define a predicate
>> to decide whether this-command-keys should be applied to
>> key bindings of the overriding temporary map or passed through
>> to other less specific keymaps.
>
> Not sure I understand.  Why do we need to look at this-command-keys?
> Are you keeping the default [t] binding in isearch-mode-map, maybe?
> That would defeat the purpose of using set-temporary-overlay-map,
> I think.

Hmm, I can't imagine how to keep the isearch-allow-scroll feature
and other conditional exiting features like search-exit-option
without keeping the default [t] binding in isearch-mode-map
to the function like the current isearch-other-meta-char
where these conditions can be checked.

Maybe the arg KEEP-PRED set-temporary-overlay-map
can be used to decide whether to exit Isearch and
apply the key sequence to global keymaps?