feat(metadata extractor): Cache the fieldMetadataExtractor for greater performance
feat(metadata extractor): Cache the fieldMetadataExtractor for greater performance

Dartium tests run in 7.6s; down from 18.2s.
dart2js on Chrome runs in 2m instead of 3m

winstonewert/angular.dart,hitesh97/angular.dart,giovannicandido/angular.dart,hitesh97/angular.dart,trinarytree/angular.dart,winstonewert/angular.dart,ronlobo/angular.dart,winstonewert/angular.dart,hitesh97/angular.dart,ronlobo/angular.dart,SibuStephen/angular.dart,SibuStephen/angular.dart,winstonewert/angular.dart,ronlobo/angular.dart,rkirov/angular.dart,trinarytree/angular.dart,SibuStephen/angular.dart,hitesh97/angular.dart,giovannicandido/angular.dart,giovannicandido/angular.dart,ronlobo/angular.dart,rkirov/angular.dart,SibuStephen/angular.dart,rkirov/angular.dart,rkirov/angular.dart,trinarytree/angular.dart,trinarytree/angular.dart