Temporal Polyfill
This is an implementation of a polyfill for the TC39 Termporal Proposal.
Implementation Issues:
Proposed Changes / Additions to the Proposal
Instant.prototype.format(locale = navigator.language, options = {}) & ZonedInstant.prototype.format(locale = navigator.language, options = {})
Considering the frequency of converting date/time values to customized strings, the format
convenience method seems to make sense. It should follow the same signature as
Intl.DateTimeFormat.prototype.format with the notable exception that locale is defaulted
to navigator.language and the timeZone option is overriddent to the ZonedInstant's time
zone or UTC for Instants.