Here are some resources that may or may not be useful:
- Gregorian Calendar object in Java: GregorianCalendar (Java Platform SE 8 )
- Source code for the ZoneInfo object in Android: luni/src/main/java/libcore/util/ZoneInfo.java - platform/libcore - Git at Google
- Overview of the tz (timezone) database from Wikipedia: tz database - Wikipedia
Some of the information you highlighted is in the GregorianCalendar object and the remainder is in the ZoneInfo object. The ZoneInfo object is a representation of the data for a particular time zone from the tz database included in your Android device.
It is also worth noting that Instants are a leaky abstraction in App Inventor since they aren't particularly well defined on our end. For example, the string version is different between the Android and iOS versions due to them being backed by different objects on the two platforms. If you're looking to parse this information from the string representation don't expect it to necessarily work across platforms and even different versions of the same platform.