feat: Move search highlighting to editor API

[elzody]

📝 Summary

• Resolves: Move search highlighting to editor API #6133

Previously, Text would emit and subscribe to events using @nextcloud/event-bus and other apps which wanted to use search highlighting would need to subscribe and emit their own corresponding events to trigger it. This was not ideal since it required apps to use some unknown / undocumented API for triggering search highlighting. This PR moves away from using the event bus for cross-app communication in this case, and allows apps to just call some search methods on the editor itself.

Please note, the event bus is still used in one area, but it is not used for cross-app communication in that case. It is used only for communicating with deeply-nested Prosemirror plugins and the editor class itself, and is thusly not exposed as something other apps can use. They must still use the editor API.

🏁 Checklist

• Code is properly formatted (npm run lint / npm run stylelint / composer run cs:check)
• Sign-off message is added to all commits
• Tests (unit, integration and/or end-to-end) passing and the changes are covered with tests
• Documentation (README or documentation) has been updated or is not required

[mejo-]

Really nice, looks great @elzody! Also extra kudos for the cypress component tests ❤️

I didn't test, but I guess you already tested this with corresponding code changes in Collectives?

I only have one nitpicking comment, otherwise good to be merged from my side.

[juliusknorr]

Nice and clean 🚀