perf: latest tsickle to tree shake: abstract class methods & interfaces (#18236)

In previous version of tsickle abstract class methods were materialized.
The change resulted in 6Kb savings in angular.io bundle.

This change also required the removal of `@private` and `@return` type
annotation as it is explicitly dissalowed by tsickle.

NOTE: removed casts in front of `makeDecorator` due to:
https://github.com/angular/devkit/issues/45

```
 14938 Jul 19 13:16 0.b19e913fbdd6507d346b.chunk.js
  1535 Jul 19 13:16 inline.d8e019ea3cfdd86c2bd0.bundle.js
589178 Jul 19 13:16 main.54c97bcb6f254776b678.bundle.js
 34333 Jul 19 13:16 polyfills.4a3c9ca9481d53803157.bundle.js

 14938 Jul 18 16:55 0.b19e913fbdd6507d346b.chunk.js
  1535 Jul 18 16:55 inline.0c83abb44fad9a2768a7.bundle.js
582786 Jul 18 16:55 main.ea290db71b051813e156.bundle.js
 34333 Jul 18 16:55 polyfills.4a3c9ca9481d53803157.bundle.js

main savings: 589178 - 582786 = 6,392
```

PR Close #18236

packages/core/src/di/metadata.ts

@@ -151,7 +151,7 @@ export interface Injectable {}
  * @stable
  * @Annotation
  */
-export const Injectable: InjectableDecorator = <InjectableDecorator>makeDecorator('Injectable');
+export const Injectable: InjectableDecorator = makeDecorator('Injectable');
 
 /**
  * Type of the Self decorator / constructor function.

packages/core/src/metadata/di.ts

@@ -201,12 +201,11 @@ export type ContentChildren = Query;
  *  @stable
  *  @Annotation
  */
-export const ContentChildren: ContentChildrenDecorator =
-    <ContentChildrenDecorator>makePropDecorator(
-        'ContentChildren',
-        (selector?: any, data: any = {}) =>
-            ({selector, first: false, isViewQuery: false, descendants: false, ...data}),
-        Query);
+export const ContentChildren: ContentChildrenDecorator = makePropDecorator(
+    'ContentChildren',
+    (selector?: any, data: any = {}) =>
+        ({selector, first: false, isViewQuery: false, descendants: false, ...data}),
+    Query);
 
 /**
  * Type of the ContentChild decorator / constructor function.

packages/core/src/metadata/directives.ts

@@ -400,7 +400,7 @@ export interface Directive {
  * @Annotation
  */
 export const Directive: DirectiveDecorator =
-    <DirectiveDecorator>makeDecorator('Directive', (dir: Directive = {}) => dir);
+    makeDecorator('Directive', (dir: Directive = {}) => dir);
 
 /**
  * Type of the Component decorator / constructor function.
@@ -683,7 +683,7 @@ export interface Component extends Directive {
  * @stable
  * @Annotation
  */
-export const Component: ComponentDecorator = <ComponentDecorator>makeDecorator(
+export const Component: ComponentDecorator = makeDecorator(
     'Component', (c: Component = {}) => ({changeDetection: ChangeDetectionStrategy.Default, ...c}),
     Directive);
 
@@ -724,8 +724,7 @@ export interface Pipe {
  * @stable
  * @Annotation
  */
-export const Pipe: PipeDecorator =
-    <PipeDecorator>makeDecorator('Pipe', (p: Pipe) => ({pure: true, ...p}));
+export const Pipe: PipeDecorator = makeDecorator('Pipe', (p: Pipe) => ({pure: true, ...p}));
 
 
 /**

packages/core/src/metadata/ng_module.ts

@@ -191,4 +191,4 @@ export interface NgModule {
  * @Annotation
  */
 export const NgModule: NgModuleDecorator =
-    <NgModuleDecorator>makeDecorator('NgModule', (ngModule: NgModule) => ngModule);
+    makeDecorator('NgModule', (ngModule: NgModule) => ngModule);

packages/core/src/util/decorators.ts

@@ -263,7 +263,8 @@ export function Class(clsDef: ClassDefinition): Type<any> {
  */
 export function makeDecorator(
     name: string, props?: (...args: any[]) => any, parentClass?: any,
-    chainFn?: (fn: Function) => void): (...args: any[]) => (cls: any) => any {
+    chainFn?: (fn: Function) => void):
+    {new (...args: any[]): any; (...args: any[]): any; (...args: any[]): (cls: any) => any;} {
   const metaCtor = makeMetadataCtor(props);
 
   function DecoratorFactory(objOrType: any): (cls: any) => any {
@@ -298,7 +299,7 @@ export function makeDecorator(
 
   DecoratorFactory.prototype.toString = () => `@${name}`;
   (<any>DecoratorFactory).annotationCls = DecoratorFactory;
-  return DecoratorFactory;
+  return DecoratorFactory as any;
 }
 
 function makeMetadataCtor(props?: (...args: any[]) => any): any {