Add 2 new `JavaTimeFeature`s: (`TRUNCATE_TO_MSECS_ON_WRITE`, `TRUNCATE_TO_MSECS_ON_READ`) for truncating `java.time` values before serialization, after deserialization

[cowtowncoder]

(note: continuation of [modules-java8#374)(https://github.com/FasterXML/jackson-modules-java8/issues/374))

Existing features

• DeserializationFeature.READ_DATE_TIMESTAMPS_AS_NANOSECONDS
• SerializationFeature.WRITE_DATE_TIMESTAMPS_AS_NANOSECONDS

allow changing unit-of-time associated with numeric (JSON Number) timestamps b/w milliseconds (false) and nanoseconds (true), in cases where Time value has granularity beyond milliseconds.
As a consequence, when disabled, precision is truncated to millisecond resolution.

These settings have no effect on textual (JSON String) representations, however.

It would be useful to have explicit features -- for this module, that'd be JavaTimeFeature (in 2.x -- in 3.x it'd be databind's new DateTimeFeature) -- like:

• JavaTimeFeature.TRUNCATE_TO_MSECS_ON_READ
• JavaTimeFeature.TRUNCATE_TO_MSECS_ON_WRITE

which would:

1. TRUNCATE_TO_MSECS_ON_READ enabled: after reading Time value, clear nanoseconds part before returning to caller (affects Numeric timestamps too)
2. TRUNCATE_TO_MSECS_ON_WRITE enabled: before writing Time value, clear nanoseconds part

These would alongside but independent @JsonFormat(pattern = ) configuration.

Due to plans for 2.x vs 3.x, this should only be considered for 3.x (3.1).

[JooHyukKim]

Given there is already way to handle expected behavior I think 3.x?

[cowtowncoder]

@JooHyukKim No, there is no truncation logic in 3.x either (aside from using @JsonFormat(pattern = ...) for serialization which is also available on 2.x).

[cowtowncoder]

Actually, I think this should only go in 3.x; too much merging work otherwise. Will transfer to jackson-databind.

[cowtowncoder]

Implemented by #5520.