PrimitiveCList optimizations

[mweidner037]

Benchmark throughout to see which ones make a difference.

• Use ids in single-element delete messages, instead of full loc
• reset: leave both ends of the range unset, loop over all values without comparisons
• For longer range deletes, find start and end indices first and then loop, instead of comparing ids each time
• For range deletes, emit bulk delete events each time you get to a non-skipped index, instead of individual events per character
• Use anchor deduplication in saved state, like in memory
• When loading, build the whole tree at once as an all-black tree, in O(n) time
• Misc TODOs in TreedocDenseLocalList
• Option to use a string in loadLocs for the values, instead of having to convert to chars and back?

[mweidner037]

Good enough for now.