Add ICU4X based calendars for Chinese and Dangun to ensure consistent behaviour
across `Intl.DateTimeFormat` and `Temporal`.
This requires using the ICU4C C++ API, so it's not possible to use when
`MOZ_SYSTEM_ICU` is defined. And ICU4X's calendar FFI needs to be available,
which is currently guarded by `JS_HAS_TEMPORAL_API`.
Differential Revision: https://phabricator.services.mozilla.com/D241645
2c4c691853