apply suffix and isearch zle_highlights on top

[m0vie]

Now that
38145: ZLE parameters for isearch and completion suffixes
got merged upstream, we can make use of these.

[danielshahaf]

So, this PR fixes #224 and moots #257, is that correct? How is this PR related to #259, I assume they are independent (both of them needed)?

[danielshahaf]

In second thought, I think we'll still need to fix #257 separately older zsh.

[m0vie]

Yes, this takes care of #224 and #257 for new versions of zsh. We can't do much for older versions, except disable highlighting in isearch altogether. #259 is completely unrelated. I was gonna close #259 because that does not have the effect I wanted it to have.