prefer_generic_function_type_aliases

PREFER generic function type aliases.

With the introduction of generic functions, function type aliases (typedef void F()) couldn't express all of the possible kinds of parameterization that users might want to express. Generic function type aliases (typedef F = void Function()) fixed that issue.

For consistency and readability reasons, it's better to only use one syntax and thus prefer generic function type aliases.

BAD:

typedef void F();

GOOD:

typedef F = void Function();