bug#47755: 27.1; mouse-yank-at-click fails

[Juri Linkov <juri@linkov.net>]

>> int main()
>> {
>>   xyzz = abcc;
>> }
>>
>> 1. Place mouse over `main` and left double click - `main` is selected
>> 2. isearch-forward (C-s) `xyzz` - `xyzz` is selected
>> 3. place cursor over `x` of `xyzz` and mouse-yank-at-click (middle mouse
>> down)
>>
>> You should see error "Lisp nesting exceeds `max-lisp-eval-depth`"
>
> It's an infinite recursion inside isearch-mouse-2.

This is because let-binding overriding-terminal-local-map to nil

  (let ((overriding-terminal-local-map nil))
    (key-binding (this-command-keys-vector) t))

doesn't disable its current value anymore.  It used to work when bug#23007
was fixed in 2017.  So in Emacs 26.3 it correctly returned 'mouse-yank-primary',
but in Emacs 27 it's broken and returns 'isearch-mouse-2' without ignoring
the current value of overriding-terminal-local-map, i.e. currently let-binding
'overriding-terminal-local-map nil' has no effect for 'key-binding'.