FB-1897
The specs for the datetimepart function are, as far as i can tell,
identical to the existing datepart function. Per Pat, replaced the
datepart function with datetimepart rather than just adding
datetimepart as an alias. Made sure existing tests that were using
datepart got switched over.
Second go at this after sorting out weirdness with git.
FB-1896
Added the datetimename function, which returns parts of a timestamp
as strings. Month and day of the week are named ("January", "Monday")
while others are returned as a string of digits ("2023").
Added tests to the test definitions.
* Removed support for EPOCH column constraint from TIMESTAMP SQL data type.
* Implicit conversion of integers to timestamp will treat the integer value as seconds since unix epoch.
* Add new ToTimeStamp(num, timeunit) SQL scalar function to help convert integer values to timestamp.
