file method
Execute file in current environment.
Maps to: .file <path>
Implementation
@override
Future<ExecuteResult> file(String path) async {
final resolved = _state.resolvePath(path);
final f = File(resolved);
if (!f.existsSync()) {
throw CliFileNotFoundException(resolved);
}
final source = f.readAsStringSync();
return executeContinued(source, basePath: f.parent.path);
}