docs(core): move headings to `@usageNotes` (#26039)

PR Close #26039

packages/core/src/di/injection_token.ts

@@ -39,11 +39,11 @@ import {defineInjectable} from './defs';
  * @usageNotes
  * ### Basic Example
  *
- * #### Plain InjectionToken
+ * ### Plain InjectionToken
  *
  * {@example core/di/ts/injector_spec.ts region='InjectionToken'}
  *
- * #### Tree-shakable InjectionToken
+ * ### Tree-shakable InjectionToken
  *
  * {@example core/di/ts/injector_spec.ts region='ShakableInjectionToken'}
  *

packages/core/src/metadata/view.ts

@@ -11,6 +11,9 @@
  *
  * See {@link Component#encapsulation encapsulation}.
  *
+ * @usageNotes
+ * ### Example
+ * {@example core/ts/metadata/encapsulation.ts region='longform'}
  */
 export enum ViewEncapsulation {
   /**
@@ -42,9 +45,6 @@ export enum ViewEncapsulation {
    * For the DOM this means using modern [Shadow
    * DOM](https://w3c.github.io/webcomponents/spec/shadow/) and
    * creating a ShadowRoot for Component's Host Element.
-   *
-   * ### Example
-   * {@example core/ts/metadata/encapsulation.ts region='longform'}
    */
   ShadowDom = 3
 }