Add describe evil ex-command functionality

[dalanicolai]

For introspection purposes it can be nice to have this functionality. Also this
function can be used to get an overview of which ex-commands are available.

[Kazark]

Slick

[dalanicolai]

Haha! Yeah it is a funny one...

[dalanicolai]

Probably quite unnecessary to refer to the already closed request #5577

[lebensterben]

If helpful layer is enabled, we can use (helpful-callable func) instead of (describe-function func).
The output is much more readable.

[dalanicolai]

Thanks for pointing out, I have added it. On the other hand, the helpful layer could make describe-function an alias for helpful-callable (and document it is aliased by the helpful layer in the docstring). Although that would probably be useful only for this single function.

[dalanicolai]

Making it an alias, also keeps the ivy-actions available. Right now, with the helpful layer, I loose the ivy actions Info and definition (which I use all the time) when using SPC h d f.

[dalanicolai]

On the other hand, I already had a personal helpful layer, where I bound the helpful function under SPC h h f (etc.) , which is an alternative solution. The command is not called describe-function anymore, but helpful-callable, so that made more sense to me...

[dalanicolai]

I would vote to change those bindings in the helpful layer

[dalanicolai]

or provide a configuration variable like helpful-prefer-alias

[smile13241324]

Looks good.

[smile13241324]

Hmmm not a bad idea about the alias in helpful layer, we just need to make sure to add the new third parameter to the alias call otherwise this will break emacs 28 again.