pid1: order units using TTYVHangup= after vconsole setup

The goal of this change is to delay getty services until after
systemd-vconsole-setup has finished. systemd-vconsole-setup starts loadkeys,
and it seems that when loadkeys is interrupted by the TTY hangup call we do
when starting tty services [1], so that loadkeys starts getting EIO from the
ioctl("/dev/tty1", KDSKBENT) syscall it does.

Fixes #26908.

[1] https://github.com/legionus/kbd/issues/92#issuecomment-1554451788

Initially I wanted to add ordering dependencies to individual units, but
TTYVHangup= can be added to other various external units too. The solution with
an implicit dependency should cover those cases too.

src/core/socket.c

@@ -276,7 +276,11 @@ static int socket_add_default_dependencies(Socket *s) {
                         return r;
         }
 
-        return unit_add_two_dependencies_by_name(UNIT(s), UNIT_BEFORE, UNIT_CONFLICTS, SPECIAL_SHUTDOWN_TARGET, true, UNIT_DEPENDENCY_DEFAULT);
+        r = unit_add_two_dependencies_by_name(UNIT(s), UNIT_BEFORE, UNIT_CONFLICTS, SPECIAL_SHUTDOWN_TARGET, true, UNIT_DEPENDENCY_DEFAULT);
+        if (r < 0)
+                return r;
+
+        return exec_context_add_default_dependencies(UNIT(s), &s->exec_context);
 }
 
 _pure_ static bool socket_has_exec(Socket *s) {