WP_Date_Query docblock doesn't properly describe array inputs

[boonebgorges]

See https://core.trac.wordpress.org/ticket/31001#comment:7 and https://core.trac.wordpress.org/attachment/ticket/31001/31001.2.patch

Many of the params in WP_Date_Query accept arrays rather than ints - and, indeed, BETWEEN and NOT BETWEEN *require* arrays - but the documentation doesn't make this clear.

[boonebgorges]

DrewAPicture - If you have a moment, could you give your feedback on 31036.diff​? The rub is that a bunch of parameters that normally require int values accept or even require array values when used in conjunction with certain values of compare. This is a hard (and redundant) thing to spell out in the array hash, so I've added a paragraph to the long description. What do you think?

[DrewAPicture]

In 31336:

Clarify inline documentation for WP_Date_Query to better explain the relationship between an individual clause's 'compare' argument and various integer-based date arguments.

If the 'compare' argument equals 'IN' or 'NOT IN', arrays of any number of specific, valid values are accepted and simply considered based on the value of 'operator' (OR or AND). If the 'compare' argument is a range such as 'BETWEEN' or 'NOT BETWEEN', arrays of only two valid values are accepted.

Props boonebgorges.
Fixes #31036.