bug#35360: 26.2; Default bindings of `A' and `Q' in Dired, for MS Windows users

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

These keys used to be bound to `dired-do-search' and
`dired-do-query-replace-regexp', by default.  Those commands, which
still exist (good), do not require a Windows user to have `find' or
`grep' OS commands available.  They require only an Emacs TAGS file.

Shouldn't the default bindings of `A' and `Q' DTRT on MS Windows out of
the box?  Why assume that Windows users have GNU/Linux commands or their
equivalents?  Can't Emacs either bind these keys to what they were bound
to previously or test first whether the requisite OS commands are
available before binding these keys to Emacs commands that won't be
usable for many Windows users?

It would be better, IMHO, to keep `A' and `Q' bound to their previous,
TAGS-based commands, and introduce new key bindings for the new xref
commands.  That would not break existing keys for MS Windows users.  And
if the availability of OS commands needed by the xref functions were
tested first then the new xref-command key bindings could be skipped if
those OS commands are not present.

In such an approach all users, on all platforms, would all once again
have the same commands for `A' and `Q'.

In GNU Emacs 26.2 (build 1, x86_64-w64-mingw32)
 of 2019-04-13
Repository revision: fd1b34bfba8f3f6298df47c8e10b61530426f749
Windowing system distributor `Microsoft Corp.', version 10.0.17134
Configured using:
 `configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static -g3''