Refactor tests; don't test for GregorianYear< 0

[afs]

Follow on from JENA-1503.

This splits up some TestTypeLiteral tests and removes the old testing for GregorianYear< 0 which didn't test correctly, and couldn't.

[ajs6f]

I can't tell what's going on here because of Git doing something really weird in terms of how it's calculating the diff... Did you add 18 new test methods, or just 1?

[afs]

Added zero. I split one mega test (testDateTime) into parts. It was a sequence of independent parts. The same testing is done so that it is easier to work on any failures. testDateTime_9 contains a change - don't touch years < 0 because of the GregorianCalendar issue.

[ajs6f]

Ok, testDateTime_9 LGTM and if the others are just cut-and-paste, it should all be good.