Backport of 1a0dddf4ad24b3f2c751a1fe0e024fdbf8754f94 (AKA #445395)
* Add support for a Range field ValuesSource, including decode logic for range doc values and exposing RangeType as a first class enum
* Provide hooks in ValuesSourceConfig for aggregations to control ValuesSource class selection on missing & script values
* Branch aggregator creation in Histogram and DateHistogram based on ValuesSource class, to enable specialization based on type. This is similar to how Terms aggregator works.
* Prioritize field type when available for selecting the ValuesSource class type to use for an aggregation
aec125faff