bug#64272: 28.1; lisp_file_lexically_bound_p behavior mismatches file local variables

[Stefan Monnier]

> So now let me turn the table and ask: if we are only going to support
> whitespace before the semicolon, then what exactly are we gaining
> here?

I think the main problem is the disconnect between the various ways the
cookie is recognized, so it may appear to work on one end and fail to
work on the other, leaving the user rather perplexed.

So maybe we should export `lisp_file_lexically_bound_p` to ELisp, let
the byte-compiler (and maybe also `emacs-lisp-mode`) verify that it
gives the same answer as `hack-local-variables-prop-line`, and emit
a loud warning if it doesn't.


        Stefan