bug#70968: 29.2.50; choose-completion on an emacs22-style completion deletes text after point

[Spencer Baugh]

try-completion and choose-completion have different behavior; with the
emacs22 completion style, the former preserves the text after point
(while ignoring it), whereas the latter deletes the text after point.

1. emacs -Q

2. In scratch, type "inhibit-asdf" and move point to after the "-"

3. Type "q" and M-<tab>
   The buffer now contains "inhibit-quitasdf", because the emacs22 style
   ignored the text after point and completed on "inhibit-q".

4. C-/ C-/ to change the buffer back to "inhibit-asdf"

5. M-<tab>
   The *Completions* buffer will be displayed, containing among others
   "inhibit-quit" as a completion, because the emacs22 style ignored the
   text after point and completed on "inhibit-".

6. Use M-<down> and M-<ret> to select and choose "inhibit-quit"
   The buffer now contains "inhibit-quit".

The two ways of selecting completions should behave the same.

I suggest that the behavior of not deleting the text after point is
better.  The emacs22 style takes care to not delete the text after point
in try-completion and in completion cycling; we should take similar care
in choose-completion.

This is especially noticeable when using minibuffer-visible-completions,
which make it easier to use choose-completion.  It's also especially
noticeable with corfu-mode, which usually automatically calls
choose-completion when finishing completion.