Add 'completions-detailed' to add prefix/suffix with 'affixation-function'

Add 'completions-detailed' to add prefix/suffix with 'affixation-function'

* doc/lispref/minibuf.texi (Completion Variables)
(Programmed Completion): Add affixation-function.

* lisp/help-fns.el (help--symbol-completion-table-affixation): New function.
(help--symbol-completion-table): Set affixation-function when
completions-detailed is non-nil.

* lisp/minibuffer.el (completion-metadata): Add affixation-function
to docstring.
(completions-annotations): Inherit from shadow with italic.
(completions-detailed): New defcustom.
(completion--insert-strings): Count string-width on all strings in
completion list.  Insert prefix and suffix.
(completion-extra-properties): Add affixation-function to docstring.
(minibuffer-completion-help): Call affixation-function.
(minibuffer-default-prompt-format): Move down closer to its use.

https://lists.gnu.org/archive/html/emacs-devel/2020-11/msg00613.html