We have C-x d, C-x 4 d, C-x 5 d and C-x t d, but only C-x C-j
and C-x 4 C-j.  My fingers try to use C-x 5 C-j, and find it isn't
there, at least biweekly.  Here is a draft patch to fill the gap.

C-x t C-j temporarily doesn't work due to #55582.

-- 
Sean Whitton