refactor(core): separate reflective injector from Injector interface

BREAKING CHANGE:
- Injector was renamed into `ReflectiveInjector`,
  as `Injector` is only an abstract class with one method on it
- `Injector.getOptional()` was changed into `Injector.get(token, notFoundValue)`
  to make implementing injectors simpler
- `ViewContainerRef.createComponent` now takes an `Injector`
  instead of `ResolvedProviders`. If a reflective injector
  should be used, create one before calling this method.
  (e.g. via `ReflectiveInjector.resolveAndCreate(…)`.

modules/angular2/test/public_api_spec.ts

@@ -169,7 +169,7 @@ var NG_CORE = [
   'PLATFORM_PIPES',
   'DebugNode',
   'DebugElement',
-  'Dependency',
+  'ReflectiveDependency',
   'DependencyMetadata',
   'Directive',
   'DirectiveMetadata',
@@ -194,10 +194,11 @@ var NG_CORE = [
   'Injectable',
   'InjectableMetadata',
   'Injector',
+  'ReflectiveInjector',
   'InstantiationError',
   'InvalidProviderError',
   'IterableDiffers',
-  'Key',
+  'ReflectiveKey',
   'KeyValueChangeRecord',
   'KeyValueDiffers',
   'NgZone',
@@ -219,9 +220,9 @@ var NG_CORE = [
   'Renderer',
   'RootRenderer',
   'RenderComponentType',
-  'ResolvedBinding:dart',
-  'ResolvedProvider:dart',
-  'ResolvedFactory',
+  'ResolvedReflectiveBinding:dart',
+  'ResolvedReflectiveProvider:dart',
+  'ResolvedReflectiveFactory',
   'Self',
   'SelfMetadata',
   'SkipSelf',