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/basic/terminal-util.c

@@ -1046,7 +1046,7 @@ int lock_dev_console(void) {
         return TAKE_FD(fd);
 }
 
-int make_console_stdio(void) {
+int make_console_stdio(bool switch_to_text) {
         int fd, r;
 
         /* Make /dev/console the controlling terminal and stdin/stdout/stderr, if we can. If we can't use
@@ -1062,7 +1062,7 @@ int make_console_stdio(void) {
                         return log_error_errno(r, "Failed to make /dev/null stdin/stdout/stderr: %m");
 
         } else {
-                reset_dev_console_fd(fd, /* switch_to_text= */ true);
+                reset_dev_console_fd(fd, switch_to_text);
 
                 r = rearrange_stdio(fd, fd, fd); /* This invalidates 'fd' both on success and on failure. */
                 if (r < 0)

src/basic/terminal-util.h

@@ -112,7 +112,7 @@ int vtnr_from_tty(const char *tty);
 
 void reset_dev_console_fd(int fd, bool switch_to_text);
 int lock_dev_console(void);
-int make_console_stdio(void);
+int make_console_stdio(bool switch_to_text);
 
 int getenv_columns(void);
 int fd_columns(int fd);