Time optimization and modernization

[ChrisJohnNOAA]

Description

GregorianCalendar->java.time (mostly ZonedDateTime). This is an improvement in performance and memory usage along with simplifying our code (there's more to be done, I was trying to keep the impact outside of Calendar2 to a minimum in this pull) and moving to a modern standard.

One important thing to note, there are 2 test datasets that were impacted by this change. I don't know how common their configuration is for real datasets, but if you are using days (or smaller) since 1592 (or any earlier time like the year 0000) for a time column, you will likely want to add the attribute:
<att name="legacy_time_adjust">true</att>
to that variable.

This should keep the variable consistent with the old way of handling datetime.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• This change requires a documentation update

Checklist before requesting a review

• I have performed a self-review of my code
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (documentation changes to be written later, though the pull description covers most of it)
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes