feat: tree-shakeable providers API updates (#22655)

Rename @Injectable({scope -> providedIn}).

Instead of {providedIn: APP_ROOT_SCOPE}, accept {providedIn: 'root'}.
Also, {providedIn: null} implies the injectable should not be added
to any scope.

PR Close #22655

packages/compiler/src/core.ts

@@ -127,7 +127,7 @@ export interface ModuleWithProviders {
   providers?: Provider[];
 }
 export interface Injectable {
-  scope?: Type|any;
+  providedIn?: Type|'root'|any;
   useClass?: Type|any;
   useExisting?: Type|any;
   useValue?: any;