Adds new fastlane lanes:
- `fastlane lint` which checks the linters
- `fastlane autocorrect` which applies the linters which can autocorrect (Rubocop, SwiftFormat)
Adds a build step to the Codegen abstract target which runs SwiftFormat in lint mode, pointing out what it's going to change when run.
Applies SwiftFormat to nearly all code -- exempts a few externally-sourced files and generated code.
Adds code coverage reports to pull requests. Enabling code coverage gathering appears to be about a 25% increase in build time, unfortunately, so just enabling it for the App/Shared targets and doing it in a separate scheme so it doesn't impact local build times.
