gud.el: Bring back the pseudo-tool-bar in text frames (bug#62041)

gud.el: Bring back the pseudo-tool-bar in text frames (bug#62041)

commit 8bb5c1bfec0929f2ba419e1c503f5acc01c336c2 accidentally
threw away the pseudo-tool-bar implemented in the text frames'
menu-bar of gud-minor-mode buffers.
Bring it back, and while we're at it, improve it so it also works
right when you have both text and GUI frames.

Also fix a misunderstanding in last change (`gud-mode-map` does need
to have a Gud menu, because `gud-mode` buffers already have it by
virtue of being in `gud-minor-mode` as well).

* lisp/progmodes/gud.el (gud-text-menu-bar-map): New keymap.
(gud-menu-mode-map): Rename from `gud-shared-mode-map`.
(gud-menu-map): Adjust accordingly.
(gud-minor-mode-map): Use them.
(gud-mode-map): Don't inherit from the shared/menu keymap.