Use ICU4X instead of unicode-normalization and unicase (#6922)

* Use ICU4X instead of unicode-normalization and unicase

* Fixup

* Remove linux-raw-sys lines

* Update idna_adapter to 1.2.1 to update to ICU4X 2.x

* Remove linux-raw-sys lines

Author: hsivonen

CHANGELOG.md

@@ -69,6 +69,9 @@
 
 ## 🦊 What's Changed 🦊
 
+### Suggest
+- Switched from `unicode-normalization` and `unicase` to ICU4X. (And updated the lock file from ICU4X 1.5 to ICU4X 2.0.)
+
 ### Android
 - Bumped the minimum SDK version to 26 (Android 8). ([#6926](https://github.com/mozilla/application-services/pull/6926)