Test different sortings for `[STRINGS]`

[Yoric]

We currently sort [STRINGS] from most used to least used. This could interfere with compression. Let's try and see if we get better results by storing them:

• by lexicographical order;
• by lexicographical order right-to-left.

[dominiccooney]

Brotli generally does well when it can make a copy from a short distance away. Sorting is a decent heuristic because it puts prefixes together. You might wring a bit more benefit out of sorting by bucketing strings into "short" and "long" and then sorting those.

[Yoric]

Experiments indicate that we can gain ~2% on samples, by doing such changes, but changing sorting order that helps some samples hurts others. To be continued...