Intl4x API refactorings. (#1023)

* add js timezone parsing

* Switch icu4x and ecma to use timezones

* fix timezone calculation time

* fixes

* extract

* Fixes

* fixes

* extract casemapping

* extract collation

* extract listformat

* extract pluralrules

* extract DisplayNames

* extract Numberformat

* extract Datetimeformat

* rename

* export all

* remove intl4x entrypoint

* replace checkmarks

* more smaller changes

* more small changes

* merge mess

* fix import

* Datetime overhaul, needs remapping of options

* more test fixes

* add set extension

* tests work

* apply fix

* Work on fixing

* ymdet looking good

* Getting better and better now

* update

* Many tests

* fixes

* works

* Full conformance testing

* Fix collation

* comment out unused

* Update display names

* fix listformat

* fix plural rules

* fixes and formats

* rename

* fix example

* fix numberformatter

* export fixes

* start adding docs

* add some docs

* more docs

* more docs

* imports

* fix imports

* Renamings and more small fixes

* Renamings and more small fixes

* docs

* renaming

* add changelog

* Update pkgs/intl4x/lib/src/collation/collation.dart

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Update pkgs/intl4x/lib/src/collation/collation.dart

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* fixes

* Add more docs

* slight changes around month styles

* Updates as per review

* fix

* fix tests

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Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>