bug#41200: Displaying a tooltip with x-show-tip gets very slow as more faces are defined

[Eli Zaretskii]

> Cc: 41200@debbugs.gnu.org, Juri Linkov <juri@linkov.net>
> From: Clément Pit-Claudel <cpitclaudel@gmail.com>
> Date: Fri, 15 May 2020 14:50:17 -0400
> 
> >>> No, I was asking why not start with it as nil and actually make a
> >>> hash-table when we first need it.
> >>
> >> Oh, I thought it would be simpler to always have a hash table instead of 
> >> having to sanity check every time.
> > 
> > What is the default size of a hash-table?
> 
> 65 entries, I think.

The number of basic faces is just 18.  Is 65 a good initial size for
that?