docs(forms): move extended text to @usageNotes (#26039)

Headings are not allowed in the basic description block.

PR Close #26039

packages/forms/src/directives/number_value_accessor.ts

@@ -20,10 +20,13 @@ export const NUMBER_VALUE_ACCESSOR: any = {
  * The accessor for writing a number value and listening to changes that is used by the
  * `NgModel`, `FormControlDirective`, and `FormControlName` directives.
  *
- *  ### Example
- *  ```
- *  <input type="number" [(ngModel)]="age">
- *  ```
+ * @usageNotes
+ * ### Example
+ *
+ * ```
+ * <input type="number" [(ngModel)]="age">
+ * ```
+ *
  * @ngModule FormsModule
  * @ngModule ReactiveFormsModule
  */