bug#62027: Subject: 29.0.60; Breaking change in forward-sentence/backward-sentence

[Drew Adams]

> > Should perhaps the return values of
> > `forward-sentence'/`backward-sentence' be documented
> > to prevent this from happening again?
> 
> Why not: Hyrum's law might have won here.  But OTOH in master,
> 'forward-sentence' is a now call to 'forward-sentence-function' that
> could be changed by the user.  Maybe should we document
> 'forward-sentence-default-function'?

Yes, but _both_ should mention the return value.
And not just "to prevent this from happening again."
Documenting this helps users use the functions.

For `forward-sentence' the doc should say that the
value of var `forward-sentence-default-function'
is called, and it returns what that function returns,
and _by default_ that is the new position (point).

Functions that have useful return values should be
documented to mention what the return value is.