bug#9054: 24.0.50; show source in other window

[Juri Linkov]

>> What I would like: Either a function that displays the source for the
>> function at point in the other window or for the *Help* buffer to open
>> the source file in the same window (i.e. the window which displays the
>> *Help* buffer).
>
> I've now introduced a `help-window-keep-selected' user option in Emacs
> 29.  When enabled, these commands will reuse the *Help* window.

I see help-function-def--button-function now uses pop-to-buffer-same-window.
Should other button types do the same?  Such as help-function-cmacro,
help-variable-def, help-face-def.

BTW, I can't find a discussion about scratch-buffer, so I'll ask here:
when I accidentally delete the *scratch* buffer, the first thing I do is
'C-x b *scratch* RET' and discover an empty buffer.  I wonder would it help
to add a '("\*scratch\*\\'" . scratch-buffer) to 'auto-mode-alist'
that will recreate it after switching to a new buffer with this name?