Upgrade to icu4x 2.0

[nicoburns]

Mozilla upstream has upgraded icu4x to 2.0, and Servo is starting to pull that in via Stylo (servo/servo#37822). We'd like to avoid duplicating icu4x in the tree if possible, so we need a mozjs that uses icu4x 2.0. This looks like it will likely be SpiderMonkey 142 from upstream, or we alternatively we could backport the change.

Servo upgrade PR: servo/servo#37823
Mozilla upgrade bugzilla issue: https://bugzilla.mozilla.org/show_bug.cgi?id=1960300