bug#73736: 31.0.50; project and therefore eglot don't work without git

[Eric Gillespie <epg@pretzelnet.org>]

(I don't use project directly, but eglot requires it, and that's
all I care about.)

1. cargo new foo
2. emacs -Q foo/src/main.rs
3. M-x rust-ts-mode RET
4. M-x eglot RET

Expected:
eglot activates.

Actual:
Error:
[eglot] Server reports (type=1): Failed to discover workspace.
Consider adding the `Cargo.toml` of the workspace to the [`linkedProjects`](https://rust-analyzer.github.io/manual.html#rust-analyzer.linkedProjects) setting.

I think the problem here is that eglot needs to provide a project
root to rust-analyzer, but 'project' only knows how to find .git
directories, which I don't have in this case.

This works in editors such as JetBrains Rover and VS Code
presumably because you have to take an "Open project" step in
those.  And I'd be OK if I had to that first in emacs, but I
could find no such option.

The closest I can find is 'project-switch-project', but it
doesn't accept arbitrary directories as input, instead only
allowing me to pick from a list it found on its own, by
scrounging around for .git directories!


In GNU Emacs 31.0.50 (build 1, x86_64-pc-linux-gnu, cairo version
 1.18.2) of 2024-10-04 built on dogato
Repository revision: ef587bf6b46b2ea3ef91b260ac2542666081260d
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101012
System Description: openSUSE Tumbleweed

Configured using:
 'configure -C --prefix=/opt/emacs-master --disable-silent-rules
 --with-x-toolkit=no --without-gsettings --with-native-compilation=no'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS HARFBUZZ JPEG LCMS2
LIBSELINUX LIBXML2 MODULES NOTIFY INOTIFY OLDXMENU PDUMPER PNG RSVG
SECCOMP SOUND SQLITE3 THREADS TIFF TREE_SITTER WEBP X11 XDBE XIM XINPUT2
XPM ZLIB

Important settings:
  value of $LC_CTYPE: en_US.UTF-8
  value of $XMODIFIERS: @im=local
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  minibuffer-regexp-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date subr-x mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
cl-loaddefs cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils rmc iso-transl tooltip cconv eldoc paren electric
uniquify ediff-hook vc-hooks lisp-float-type elisp-mode mwheel
term/x-win x-win term/common-win x-dnd touch-screen tool-bar dnd fontset
image regexp-opt fringe tabulated-list replace newcomment text-mode
lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch
easymenu timer select scroll-bar mouse jit-lock font-lock syntax
font-core term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese eucjp-ms cp51932 hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting font-render-setting cairo xinput2 x multi-tty
move-toolbar make-network-process emacs)

Memory information:
((conses 16 39589 10289) (symbols 48 5375 0) (strings 32 12072 1444)
 (string-bytes 1 289442) (vectors 16 9304)
 (vector-slots 8 103508 8407) (floats 8 25 4) (intervals 56 260 0)
 (buffers 992 10))