Make taking a global lock automatically initialize locking if needed

Make taking a global lock automatically initialize locking if needed

This lets them be thread-safe by default, at the cost that they can
now fail.

init_uninitialized_locks() and init_global_locks() must now both
reimplement the equivalent of _dbus_register_shutdown_func(), by using
_dbus_platform_rmutex_lock() on the same underlying mutex around a call
to _dbus_register_shutdown_func_unlocked().

This is because if they used the usual _DBUS_LOCK() API (as
_dbus_register_shutdown_func() does), it would automatically try to
initialize global locking, leading to infinite recursion.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=54972
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Reviewed-by: Alban Crequy <alban.crequy@collabora.co.uk>
Reviewed-by: Anas Nashif <anas.nashif@intel.com>