Fix timezone handling on Windows to report POSIX timezone names

For JDBC/Node.js drivers at least, it is necessary to handle timezone information (system_time_zone, @session.time_zone) in the way that is independent from the underlying OS, and also POSIX locale names have to be supported. Currently, POSIX locale names are not accepted, and the server would report a rather unusable "Coordinated Universal Time".

The task is to make Windows behave like the other OSes do wrt to timezone information.
The mapping between Windows timezone names and POSIX is given by the "golden standard"

CLDR data https://unicode.org/repos/cldr/trunk/common/supplemental/windowsZones.xml

We can parse that to create map the names. It is also possible to find the DST setting and UTC offsets using Windows APIs GetTimezoneInformation etc.