Fair amount of typos spotted and fixed. Some of them are in comments, some of them are in code and some of them are in nondart files.

There is no need for issues since it's a typo fix.

I have doubts about [packages/flutter_tools/lib/src/ios/core_devices.dart](https://github.com/flutter/flutter/compare/master...anisalibegic:flutter:master#diff-fdbc1496b4bbe7e2b445a567fd385677af861c0093774e3d8cc460fdd5b794fa), I have a feeling it might broke some things on the other end, even though it's a typo.