Similar to the previous commit with property bags, many existing tests use
a Proxy to test the order of observable operations which involve user code
passed in as part of a Temporal.TimeZone object. I am going to write
several more tests that do this, as well. This seems like a good thing to
put into TemporalHelpers, where it can be implemented consistently so that
we don't get discrepancies in which operations are tracked.
Updates existing tests to use this helper.
