Remove mapping.date.round_ceil setting for date math parsing

[rjernst]

The setting mapping.date.round_ceil (and the undocumented setting
index.mapping.date.parse_upper_inclusive) affect how date ranges using
lte are parsed. In #8556 the semantics of date rounding were
solidified, eliminating the need to have different parsing functions
whether the date is inclusive or exclusive.

This change removes these legacy settings and improves the tests
for the date math parser (now at 100% coverage!). It also removes the
unnecessary function DateMathParser.parseTimeZone for which
the existing DateTimeZone.forID handles all use cases. The one caveat
is handling malformed H:MM values, but this is a recently added
feature, and I don't think we should have our own special format here,
but instead enforce the standard [+-]HH:MM.

Any user previously using these settings can refer to the changed
semantics and change their query accordingly. This is a breaking change
because even dates without datemath previously used the different
parsing functions depending on context.

closes #8598

[rjernst]

Note that there are a bunch of integration tests scattered around that are testing date math. Given the much better unit tests here now, I would like to remove the majority of them, leaving only basic checks of date math integration, but leaving extensive testing for the format to the unit tests. However, I do not yet have that change here, but wanted to first get a feel for opinions on their removal.

[jpountz]

The change looks good to me. Big +1 on removing all the scattered date-math tests and focusing on having good unit tests in only one or two test suites.

[rjernst]

@jpountz I've removed some tests. Let me know if you think I went to far...or not far enough.

[jpountz]

@rjernst LGTM