feat(drawer): Make list instance publicly accessible (#4516)

(cherry picked from commit f46941c)

Author: kfranqueiro

packages/mdc-drawer/component.ts

@@ -68,6 +68,10 @@ export class MDCDrawer extends MDCComponent<MDCDismissibleDrawerFoundation> {
   private handleKeydown_!: SpecificEventListener<'keydown'>; // initialized in initialSyncWithDOM()
   private handleTransitionEnd_!: SpecificEventListener<'transitionend'>; // initialized in initialSyncWithDOM()
 
+  get list(): MDCList | undefined {
+    return this.list_;
+  }
+
   initialize(
       focusTrapFactory: MDCDrawerFocusTrapFactory = createFocusTrap as unknown as MDCDrawerFocusTrapFactory,
       listFactory: MDCListFactory = (el) => new MDCList(el),

test/unit/mdc-drawer/mdc-drawer.test.js

@@ -28,7 +28,7 @@ import td from 'testdouble';
 
 import {MDCDrawer} from '../../../packages/mdc-drawer/index';
 import {strings, cssClasses} from '../../../packages/mdc-drawer/constants';
-import {MDCListFoundation} from '../../../packages/mdc-list/index';
+import {MDCList, MDCListFoundation} from '../../../packages/mdc-list/index';
 import {MDCDismissibleDrawerFoundation} from '../../../packages/mdc-drawer/dismissible/foundation';
 import {MDCModalDrawerFoundation} from '../../../packages/mdc-drawer/modal/foundation';
 
@@ -150,6 +150,11 @@ test('#set open false calls foundation.close', () => {
   td.verify(mockFoundation.close(), {times: 1});
 });
 
+test('#get list returns MDCList instance when DOM includes list', () => {
+  const {component} = setupTest();
+  assert.instanceOf(component.list, MDCList);
+});
+
 test('click event calls foundation.handleScrimClick method', () => {
   const {root, mockFoundation} = setupTestWithMocks({variantClass: cssClasses.MODAL});
   const scrimEl = root.querySelector('.mdc-drawer-scrim');