docs(docs-infra): API doc content rendering fixes (#60116)

The PR introduces a few doc content rendering fixes:
- Fix highlighted section heading styles (regression from #59965).
- Convert JSDoc links within 'Usage Notes' sections to HTML and render them.
- Add IDs to doc content headings. This, by itself, makes these headings available in the page ToC.

PR Close #60116

packages/core/src/application/application_ref.ts

@@ -188,7 +188,6 @@ export function optionsReducer<T extends Object>(dst: T, objs: T | T[]): T {
  * A reference to an Angular application running on a page.
  *
  * @usageNotes
- * {@a is-stable-examples}
  * ### isStable examples and caveats
  *
  * Note two important points about `isStable`, demonstrated in the examples below:

packages/upgrade/static/src/upgrade_module.ts

@@ -36,7 +36,7 @@ import {NgAdapterInjector} from './util';
  *    {@link UpgradeModule#upgrading-an-angular-1-service Upgrading an AngularJS service} below.
  * 4. Creation of an AngularJS service that wraps and exposes an Angular injectable
  *    so that it can be injected into an AngularJS context. See `downgradeInjectable`.
- * 3. Bootstrapping of a hybrid Angular application which contains both of the frameworks
+ * 5. Bootstrapping of a hybrid Angular application which contains both of the frameworks
  *    coexisting in a single application.
  *
  * @usageNotes
@@ -102,7 +102,7 @@ import {NgAdapterInjector} from './util';
  *
  * ### Examples
  *
- * Import the `UpgradeModule` into your top level {@link NgModule Angular `NgModule`}.
+ * Import the `UpgradeModule` into your top level Angular {@link NgModule NgModule}.
  *
  * {@example upgrade/static/ts/full/module.ts region='ng2-module'}
  *
@@ -116,7 +116,6 @@ import {NgAdapterInjector} from './util';
  *
  * {@example upgrade/static/ts/full/module.ts region='bootstrap-ng2'}
  *
- * {@a upgrading-an-angular-1-service}
  * ### Upgrading an AngularJS service
  *
  * There is no specific API for upgrading an AngularJS service. Instead you should just follow the