bug#30539: 26.0; `char-displayable-p' is much slower in Emacs 25 and 26

[Drew Adams]

Can someone please confirm that they can repro this problem?

I do have many fonts installed on my system.  Dunno whether
the recipe from `emacs -Q' has a different effect if you
do or don't have certain fonts installed.  But if not then
I think you should be able to easily and quickly repro the
problem.

Thx.