Support bracket enclosed names in TZ POSIX rules

Support bracket enclosed names in TZ POSIX rules

The POSIX time zone rules at the end of a tzfile have been updated to allow digits, plus signs and minus signs in the time zone names by enclosing the name in `<` and `>` characters. TimeZoneInfo's parsing logic was written using an older version of the spec, so it didn't have support for this format.

Fix https://github.com/dotnet/corefx/issues/16962

Commit migrated from https://github.com/dotnet/coreclr/commit/4bcc0d5d9e8870bfb579c069c2d5b4dd3b4b3b1e