* lisp/progmodes/compile.el: Allow 'line' functions in error-regexp-alist

* lisp/progmodes/compile.el: Allow 'line' functions in error-regexp-alist

(compilation-error-properties): Allow 'line' and 'end-line' to be functions,
like 'col' and 'end-col'.
(compilation-error-regexp-alist): Document this.
(compilation-parse-errors): Drop support for old undocumented feature
where 'line' was a function of 2 arguments.
(compilation--compat-error-properties): Delete function.