Use base prefix and suffix instead of completion-base-position (bug#49931)

Use base prefix and suffix instead of completion-base-position (bug#49931)

* lisp/minibuffer.el (minibuffer-completion-help):
Set completion-base-affixes from base-prefix and base-suffix.
In completion-list-insert-choice-function handle
string values of start/end as prefix/suffix.

* lisp/simple.el (completion-base-affixes)
(completion-use-base-affixes): New variables.
(choose-completion): Let-bind base-affixes to completion-base-affixes.
Use base-affixes when completion-use-base-affixes is non-nil.
(completion-setup-function): Sync values of base-affixes and
completion-base-affixes.