Functionality to support testing of Time zone offset

[bryantaustin13]

This depends on the cql-tests PR cqframework/cql-tests#88 (comment) which contains the CQLTimeZoneOffsetTest.xml.
Adds functionality to test timezone offsets. See the README for more information.

[cmoesel]

I'm not sure I understand the premise of the offset timezone policy. In the description of the timezone offset policy in this PR's README, it says:

These settings are required because CQL allows DateTime values without a timezone offset, and different engines interpret those values differently.

and...

A DateTime like this:

@2012-04-01T00:00

has no timezone offset.

When a CQL engine evaluates this, it must decide:
👉 Should this value be treated as having a timezone, or not?

I don't think there should be any ambiguity here. The CQL specification is pretty clear about this (emphasis mine):

Only DateTime values may specify a timezone offset, either as UTC (Z), or as a timezone offset. If no timezone offset is specified, the timezone offset of the evaluation request timestamp is used.

So engines always treate DateTimes as having a timezone offset; it's just a question of which timezone offset (and that's indicated by the evaluation request timestamp).

Am I misunderstanding what the README is trying to say?

[bryantaustin13]

Please look at this again and let me know if this works and any changes you would like.