bug#41862: 27.0.91; Isearch menu added to menu-bar

[Drew Adams <drew.adams@oracle.com>]

Starting with Emacs 27, `isearch-mode-map'
includes`isearch-menu-bar-map', which adds menu `Isearch' to the
menu-bar.

This should at least be optional, via user option (not requiring a user
to fiddle with keymaps).

emacs -Q

1. Resize the frame with your mouse, to make it narrower - just wide
enough to show the existing menu-bar menu names.

2. `C-s'

This causes the frame to be redisplayed to add menu-bar menu `Isearch',
which, in effect, moves everything down a line visually, because it
causes the menu-bar to wrap (since the frame was only wide enough to
show the menu-bar without the added `Isearch'.

3. `C-g', or otherwise end Isearch.

This causes the frame to be redisplayed to remove menu-bar menu
`Isearch', with the inverse jarring redisplay.

This behavior is intolerable.  At least let users disable it easily,
with an option.  A better solution than that should be found, but until
then, please at least do that.

The added user option might be only binary: (dis)allow menu `Isearch'.
Or it might have a third value that lets menu `Isearch' be added only if
there's room for it without wrapping.  In that case, the doc needs to be
very clear, so users don't wonder why `Isearch' may sometimes appear and
sometimes not.

If this jarring behavior is platform-dependent, the consider taking care
of it only for platforms where it manifests.  It's a problem for MS
Windows, at least.

In GNU Emacs 27.0.91 (build 1, x86_64-w64-mingw32)
 of 2020-04-20
Repository revision: c36c5a3dedbb2e0349be1b6c3b7567ea7b594f1c
Windowing system distributor `Microsoft Corp.', version 10.0.18362
Configured using:
 `configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static''