This uses ICU for the Intl.DateTimeFormat `format` `formatToParts`,
`formatRange`, and `formatRangeToParts`.
This lets us remove most data from our date-time format generator. All
that remains are time zone data and locale week info, which are relied
upon still for other interfaces. So they will be removed in a future
patch.
Note: All of the changes to the test files in this patch are now aligned
with other browsers. This includes:
* Some very incorrect formatting of Japanese symbols. (Looking at the
old results now, it's very obvious they were wrong.)
* Old FIXMEs regarding range formatting not including the start/end date
when only time fields were requested, but the dates differ.
* Day period inconsistencies.
Note: We keep locale parsing and syntactic validation as-is. ECMA-402
places additional restrictions on locales above what is required by the
Unicode spec. ICU doesn't provide methods that let us easily check those
restrictions, whereas LibLocale does. Other browsers also implement
their own validators here.
This introduces a locale cache to re-use parsed locale data and various
related structures (not doing so has a non-negligible performance impact
on Intl tests).
The existing APIs for canonicalization and display names are pretty
intertwined, so they must both be adapted at once here. The results of
canonicalization are slightly different on some edge cases. But the
changed results are actually now aligned with Chrome and Safari.
