Sort Localization generation output (#44743)

* Sort Localization generation output

- When creating locales that were assumed from existing locales, the
file that is used is non-deterministic. This adds a sort to the iterator
to ensure that the same existing locale is used to generate the assumed
locale
- When generating material, cupertino and date localizations, the generated getters were not sorted. This
introduces an alphabetic sort

* remove main.dart.snapshot