bug#43702: Emacs master: Incorrect highlighting in regexp isearch.

[Juri Linkov]

>> Maybe better to do what Drew proposed: to distinguish the odd groups
>> from the even groups, i.e. to have only 2 additional faces
>> (a brighter face like the current isearch-group-1 for the odd groups,
>> and a darker face for the even groups).
>
> To be clear, I didn't propose that.  My code has 8 levels
> (groups), with 8 faces.

My intention was to give credit where credit is due.
Thank you for the idea.

> What I mentioned about even and odd is for lazy-highlighting.

Both ordinary and lazy-highlighting matches could be based on
the same idea of odd/even faces.