Show correct button glyph for interact if Enter/E are not split

I thought 2.2 already had separate map and interact gamepad bindings,
and they simply got neglected and broken with 2.3's split Enter/E key
option. But actually, the new split Enter/E option also applied to
gamepad buttons, and a separate interact binding was added, without
really indicating anything if Enter and E are not split. And I guess
using the same button for map and interact by default also makes sense
for simplicity...

This commit makes sure the button glyph displayed in-game is at least
the correct button. The gamepad bindings menu is also slightly modified
to darken the interact option - the button glyphs code now
automatically causes them to show equal buttons anyway, so it wasn't
too big of a change to also darken the line and disable the binding
option. To me this says: "the interact key is fixed to be the same as
enter right now, but there is a way to change it."

It's still not ideal of course, and I know a similar change to the
gamepad menu to hide the interact option was rejected a year ago
because action sets would already fix it, but it's a year later now,
and showing misleading button glyphs should be fixed in 2.4, whether it
will already have action sets or not (And at this point I think the
plan already is to keep the existing input system for 2.4)

And it's a 3 line diff to darken and disable the option, compared to
fully hiding the option.

desktop_version/src/Game.cpp

@@ -6531,7 +6531,7 @@ void Game::createmenu( enum Menu::MenuName t, bool samemenu/*= false*/ )
         option(loc::gettext("bind enter"));
         option(loc::gettext("bind menu"));
         option(loc::gettext("bind restart"));
-        option(loc::gettext("bind interact"));
+        option(loc::gettext("bind interact"), separate_interact);
         option(loc::gettext("return"));
         menuyoff = 0;
         maxspacing = 10;