bug#42256: 27.0.50; composition

[Juri Linkov]

> If someone wants or needs to know which characters participated in a
> composition on a GUI frame, they can go to those characters in the
> *Help* buffer and type "C-u C-x =".

It's what I'm doing all the time:

1. type "C-u C-x ="
2. move point to the combining character
3. type "C-u C-x =" again

This takes too much time.

> That said, if someone wants to work on adding the character names to
> the GUI display as well, I won't object.

Ok, done on master in commit 46a0c115f0.