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.
