Now that Dart 1 is turned off, reapplying my change to turn on the prefer_generic_function_type_aliases analysis option, and fix all the typedefs to Dart 2 preferred syntax.
Also eliminated the unused analysis_options_repo.yaml file and turned on public_member_api_docs in analysys_options.yaml.
No logic changes, just changing the typedef syntax for all typedefs, and updating analysis options.
This class lives in the Context and allows callers to "inject"
flag values, where flag values are first extracted from the
command arguments, then from the global arguments as a fallback.
