bug#20164: 25.0.50; Do not tell users that `x-show-tip' is internal

[Drew Adams <drew.adams@oracle.com>]

> So perhaps the way forward here is to make `x-max-tooltip-size' an
> obsolete alias for a new variable `tooltip-max-size'?  And add a way to
> specify the FRAME parameter somehow...  but the calling convention for
> that function is kinda meh.

I guess you're asking others.  If you're also
asking me then my answer is in the bug report.
To be specific:

1. Yes, rename `x-max-tooltip-size' as you suggest.
2. Don't make `x-show-tip' internal or tell users
   it's internal.
3. Don't point users of `x-show-tip' to
   `tooltip-show'.  That's not at all the same
   thing.  Just rehabilitate `x-show-tip'.
4. If you want to rename all of the `x-*' stuff
   to remove that prefix, fine by me (assuming
   `x-*' aliases for backward compatibility).