Add support for zzzz (and beyond) in format_datetime

[kevinwilfong]

Summary: This diff adds support for JODA's zzzz (or more) patterns (all equivalent) in Presto's forma_datetime function.

This is used to format long time zone names.

Long time zone names are not available from the IANA time zone database, so we can't use the tz library to generate these. Fortunately, unicode provides some utilities to generate these.

Differential Revision: D64795407