bug#32990: 26.1.50; isearch-forward + t-m-m/mark-active doc

[charles@aurox.ch (Charles A. Roelli)]

Now that we have all of the important isearch commands and bindings
indexed, we should be able to shorten isearch-forward's docstring.
The question is, how much?  Here's one attempt that may cut out too
much:

  "Do incremental search forward for a string as you type.
\\<isearch-mode-map>
\\[isearch-repeat-forward] moves forward to the next search hit.
\\[isearch-repeat-backward] moves backward to the previous search hit.
\\[isearch-abort] aborts the search and returns point to its former position.
\\[isearch-exit] exits the search and leaves point where it is.

Many other non-printing keys have special bindings while searching;
Info node `(emacs)Incremental Search' and its descendants describes
them.

If REGEXP-P is non-nil (or interactively, when called with a
prefix argument), do an incremental regular expression search
instead.

If NO-RECURSIVE-EDIT is non-nil (as it is interactively), do not
enter a recursive edit.  If nil, enter a recursive edit and
exit the recursive edit when the search is done."

It covers the absolute basics, but leaves everything else to the
manual.  I'm not sure all users will like that, since the current
docstring covers almost all of the keybindings.

I remember reading somewhere a suggestion for adding a toolbar (and
(or) a dedicated menu) for use during isearch-mode, to help the
discoverability of these myriad keybindings.  That could be a good
alternative to listing verbosely every binding in the docstring.