RFC: improve showMatchesPosition

[flevi29]

showMatchesPosition is closely related to highlights, and it could be a better alternative. As of right now it doesn't respect searchableAttributes, attributesToHighlight, attributesToRetrieve, attributesToCrop, cropLength, but it could very well support all of these.
In fact showMatchesPosition, when enabled, should entirely replace _formatted, which should not be computed at all, this would further speed up Meilisearch, offloading the task of string manipulation to the frontend. If you're using showMatchesPosition, my thinking is that you're not touching _formatted either way.

Also, as far as I'm aware current implementation doesn't escape highlight tags, so there's always a slight chance that this could cause issues, but I haven't fully confirmed this just yet.
Also highlights are meant to be interpreted as HTML, so modern frameworks do a lot of work to sanitize it. This means that we could increase both backend and frontend performance with this.

I have previously worked on highlights (meilisearch/meilisearch#4928), I would like to attempt to make this RFC a reality as well, if I know there is interest from the Meilisearch team.

[macraig]

Hi @flevi29 , thank you for your willingness to help us improve Meilisearch ❤️ We'll happily accept your contribution to improve the feature, let us know if you have any questions or need a review.