Unify highlighting and sorting

[PythonNut]

Currently, flx-score is called twice on each candidate, once for highlighting and once for sorting. This is obviously not ideal.

It would be nice to find a way to reuse the result of the scoring for both passes. This should lead to a ~2x performance improvement. Unfortunately, this is difficult because the two passes are very strongly abstracted from each other. This will likely take a deep dive into helm's source code.

[PythonNut]

I see two ways of doing this:

1. Cache the result in a text property attached to the candidate.
2. Find a root helm function and let bind the cache variable there.