refactor(core/testing): make MatOptionHarness extend ContentContainerComponentHarness (#27766)

This allows users to obtain harnesses for more complex elements inside of the MatOption.

Author: JankaSvK

src/material/core/testing/option-harness.ts

@@ -7,14 +7,14 @@
  */
 
 import {
-  ComponentHarness,
   ComponentHarnessConstructor,
+  ContentContainerComponentHarness,
   HarnessPredicate,
 } from '@angular/cdk/testing';
 import {OptionHarnessFilters} from './option-harness-filters';
 
 /** Harness for interacting with an MDC-based `mat-option` in tests. */
-export class MatOptionHarness extends ComponentHarness {
+export class MatOptionHarness extends ContentContainerComponentHarness {
   /** Selector used to locate option instances. */
   static hostSelector = '.mat-mdc-option';
 

tools/public_api_guard/material/core-testing.md

@@ -7,6 +7,7 @@
 import { BaseHarnessFilters } from '@angular/cdk/testing';
 import { ComponentHarness } from '@angular/cdk/testing';
 import { ComponentHarnessConstructor } from '@angular/cdk/testing';
+import { ContentContainerComponentHarness } from '@angular/cdk/testing';
 import { HarnessPredicate } from '@angular/cdk/testing';
 
 // @public
@@ -19,7 +20,7 @@ export class MatOptgroupHarness extends ComponentHarness {
 }
 
 // @public
-export class MatOptionHarness extends ComponentHarness {
+export class MatOptionHarness extends ContentContainerComponentHarness {
     click(): Promise<void>;
     getText(): Promise<string>;
     static hostSelector: string;