feat: add zebra-stripe option

[noahbald]

This PR adds zebra-striping in response to #12655

• display horitonzal highlights for every other line

[noahbald]

Not sure if docs should be updating, I ran cargo xtask docgen and no changes were emitted.
Do I need to update docs and themes manually?

[nik-rev]

So I first thought this looks odd, but honestly I can see myself using this. I really like this addition!

[drybalka]

I don't want to sound negative, but doesn't it fare too far into the plugin territory? This adds yet another config option that needs to be documented (and then read by users) and requires every color theme to provide zebra-stripe highlight.

[noahbald]

I don't want to sound negative, but doesn't it fare too far into the plugin territory? This adds yet another config option that needs to be documented (and then read by users) and requires every color theme to provide zebra-stripe highlight.

I think that's fair, I wasn't too sure either. I made this mainly because it's a must-have for me to be comfortable in an editor and I want to be able to use it in my fork, as others may want.
If the priority is to keep the core editor minimal I'm happy to close the PR and wait until plugins are ready if that's more ideal