New command 'minibuffer-set-completion-styles'

New command 'minibuffer-set-completion-styles'

Add an interactive command for setting completion styles in the
current minibuffer.

* lisp/minibuffer.el (completion-style)
(completion--matching-style, completion-local-styles): New vars.
(completion--styles): Use 'completion-local-styles' when it's non-nil.
(completion--nth-completion): Set 'completion--matching-style' to the
matching completion style.
(completion-styles-affixation, completion-styles-table): New funs.
(minibuffer-set-completion-styles): New command.
(minibuffer-local-completion-map): Bind it.
(minibuffer-completion-help): Set 'completion-style' in the
"*Completions*" buffer.
* lisp/simple.el (completion-setup-function): Keep 'completion-style'.
(completion-list-mode): Display 'completion-style' in mode line.

* doc/emacs/mini.texi (Completion Commands, Completion Styles):
Document new command.

* doc/lispref/minibuf.texi (Completion Commands)
(Completion Variables): Document new command and variable.

* etc/NEWS: Announce new command.