Improve Date precision truncation handling

[PSeitz]

The way we handle precision truncation of DateTime when querying is opaque and error-prone. When using a date in the inverted index we want to truncate it to seconds, since they are all stored with second precision. In the columnar storage the precision is configurable.

Currently DateTime is stored truncated in Term, but this is not great since we don't know if Term is used in the inverted index or columnar.

Ideally we would store DateTime with full precision and get a truncated version before using it in a query. E.g range queries may use the inverted index or the columnar storage.

Related: #2456
Depends on splitting term into indexing term and term: #2366