* Move firebase user agent logic to a separate class.
* FIRAppTest: prefix some tests with the tested method names
* FIRAppTest: user agent new fields tests
* New user agent field added.
* Headers
* API docs
* ./scripts/style.sh
* nullability fix
* Move environment info methods to GoogleUtilities
* GULAppEnvironmentUtilTest
* GULAppEnvironmentUtil swift tests
* FirebaseApp user agent swift flag test
* ./scripts/style.sh
* Cleanup CoreDiagnostics
* Nullable device model
* FIRCoreDiagnosticsTest fix
* Merge fixes
* Fix import
* rename
* Cleanup GUL imports (since all headers are public now)
* Remove the `FirebaseOptions()` bare initializer.
This was unintentionally surfaced from the ObjC header and should be
removed.
Note: although the existing initializer doesn't work, this is still a
breaking change.
* Style
* Changelog update.
Maksym Malyhin