shutdown: preserve console graphics mode across the exitrd handoff

make_console_stdio() forces KD_TEXT while reopening /dev/console. When
systemd-shutdown enters the exitrd, this can expose the text console over
a retained graphical shutdown splash.

Let callers choose whether to switch to text mode, and preserve the mode
for the exitrd handoff. Keep the existing text-mode behavior for manager
reexecution and the crash shell. Restore text mode if executing /shutdown
fails and before reporting a fatal error and freezing.

Add an unsafe, nonparallel virtual-console regression test requiring
explicit opt-in and an already-owned inactive VT in a disposable VM.
Check graphics preservation and text restoration through a private
/dev/console bind mount, retain stderr diagnostics, and restore the saved
mode in the parent even if the child fails.

src/core/main.c

@@ -2331,7 +2331,7 @@ static int do_reexecute(
                 log_warning_errno(r, "Failed to move /run/systemd/ to /run/systemd.pre-switch-root/, ignoring: %m");
 
         /* Reopen the console */
-        (void) make_console_stdio();
+        (void) make_console_stdio(/* switch_to_text= */ true);
 
         i = 1;         /* Leave args[0] empty for now. */
         for (int j = 1; j <= argc; j++)