bug#29478: 26.0.90; `C-h k' followed by mouse clicks no longer shows down event

[Eli Zaretskii]

I think I found one more problem with Help functions on mouse clicks.
Try this in "emacs -Q":

  C-h c S-mouse-1
  C-h k S-mouse-1

In Emacs 25.2 these produce the description of mouse-appearance-menu,
as expected, saying it's the binding of S-down-mouse-1.  Emacs
26.0.90 does the same for "C-h c", but claims S-mouse-1 is undefined
if you invoke "C-h k".  The current emacs-26 branch claims S-mouse-1
is undefined for both "C-h c" and "C-h k".

I think this means that we have similar problems with any explicit
bindings to S-down-mouse-N clicks.

This is a regression that I think we must fix before releasing Emacs
26.1.