resolve method
Resolves a module.
path is the path of the module (as returned by calling resolvePath)
Returns null if the module was not found.
Implementation
@override
Future<ResolvedModule> resolve(String path) async {
final file = File(path);
final script = await file.readAsString(encoding: encoding);
final result = parser.parse(script);
return ResolvedModule.fromParseResult(result);
}