Corects a bnuch of typeos throuhgout teh Fluter codebsae.

Made use of the `misspell` tool:
https://github.com/client9/misspell

Cupertino localization step 8: create a gen_cupertino_localizations and generate one for cupertino english and french (#29824)

Cupertino localization step 7: modularize material specific things out of gen_localizations.dart (#29822)

Cupertino localization step 4: let generated date localization combine material and cupertino locales (#29650)

Cupertino localization step 3: in-place move some material tools around to make room for cupertino (#29644)