bug#44529: [PATCH] Convert apropos-internal from C to Lisp

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Mon, 9 Nov 2020 02:38:59 -0800
> Cc: monnier@iro.umontreal.ca
> 
> > I discovered that apropos-internal is defined in keymap.c for a reason
> > that escapes me (it really should be moved to apropos.el).
> 
> Yes.  So I was actually going to propose the attached patch.  In my
> testing, it is as fast as the C version (especially when byte-compiled),
> which would match my intuition from reading the code.
> 
> (benchmark-run 10
>   (apropos-command "test"))
> => (0.12032415399999999 2 0.014772391999999995) ; C
> => (0.13513192100000002 2 0.017216643000000004) ; Lisp
> 
> (benchmark-run 10
>   (apropos "x"))
> => (3.846117816 131 1.092690677) ; C
> => (4.218219444 145 1.2153865740000003) ; Lisp

20% slowdown is not negligible, at least not in principle.  Let's wait
for more people to voice their opinions on this aspect.

> Any comments or objections?

A bother: apropos.el is not preloaded, so please double-check that
none of the preloaded files call apropos-internal, otherwise that
would mean we need to preload apropos.el, which I think is
undesirable.

Thanks.