Give affixation-function higher priority over annotation-function (bug#45234)

Give affixation-function higher priority over annotation-function (bug#45234)

* doc/lispref/minibuf.texi (Completion Variables)
(Programmed Completion): Describe precedence rules
of affixation-function and annotation-function.

* lisp/minibuffer.el (completion-metadata)
(completion-extra-properties): Describe precedence rules
of affixation-function and annotation-function.
(minibuffer-completion-help): First try to apply
affixation-function, if there is no such function,
try annotation-function.