Handle point not at EOB in minibuffer-choose-completion

Handle point not at EOB in minibuffer-choose-completion

Without this change, only the minibuffer contents before point
are cleared when a completion is chosen, which results in stray
text when point is in the middle of the minibuffer.

After this change, we heuristically decide either to clear the
whole buffer or only part of it, taking into account the
location of point.

This is a backport for the Emacs 29 release branch of a simpler
fix in minibuffer-completion-help.

* lisp/minibuffer.el (minibuffer-next-completion):
(minibuffer-choose-completion):
Recalculate completion-base-affixes with point.  (Bug#62700)