Handle all from and to relative dates in API4

[larssandergreen]

Overview

API4 does not work correctly with relative dates that are open ended (e.g. From start of current calendar year). The open ended date is set to NULL here and then that is somewhere converted to a 0 timestamp, so one side of the comparison is Jan 1, 1970. That works half the time and doesn't work the other half of the time (when the To date is 1970).

Before

The unspecified date was set to 0.

After

Open ended relative date API calls with =, !=, <>, LIKE or NOT LIKE are converted to >= or <= as appropriate.
Nothing is changed for BETWEEN or NOT BETWEEN calls.

Technical Details

It is possible (for example in Search Kit) to specify a BETWEEN with relative date ranges as the From and To dates. That works fine in general, but won't work with half of the open ended relative dates. Such a query is pretty nonsensical and I don't think we need to worry about what it returns.

It would have been nice if BETWEEN date and NULL was equivalent to >= date in SQL, but it isn't.

[civibot]

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[colemanw]

@larssandergreen this makes a lot of sense but really needs a unit test. You could just add a few more cases to \api\v4\Action\DateTest.

[larssandergreen]

@colemanw Tests added.