Change numeric data types to use SORTED_NUMERIC docvalues type

Change numeric data types to use SORTED_NUMERIC docvalues type instead of a custom encoding in BINARY.

In low level benchmarks this is 2x to 5x faster: its also optimized for the common case where fields actually only contain at most one value for each document.

Additionally SORTED_NUMERIC doesn't lose values if they appear more than once, so mathematical computations such as averages are correct.

I think we should open an issue about these null settings, that's worrying!