Similar to the previous commits with property bags and time zones, there
are also some existing tests that 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, or bugs due to
a Symbol-valued property.
Updates existing tests to use this helper.
ae52931aae