fix(material/bottom-sheet): aria-modal not being set

Fixes that `aria-modal` wasn't being set on the bottom sheet container. This likely broke when the bottom sheet was refactored to use the CDK dialog.

(cherry picked from commit 90e6446)

src/material/bottom-sheet/bottom-sheet-config.ts

@@ -44,6 +44,9 @@ export class MatBottomSheetConfig<D = any> {
   /** Aria label to assign to the bottom sheet element. */
   ariaLabel?: string | null = null;
 
+  /** Whether this is a modal bottom sheet. Used to set the `aria-modal` attribute. */
+  ariaModal?: boolean = true;
+
   /**
    * Whether the bottom sheet should close when the user goes backwards/forwards in history.
    * Note that this usually doesn't include clicking on links (unless the user is using

src/material/bottom-sheet/bottom-sheet-container.ts

@@ -47,7 +47,7 @@ import {matBottomSheetAnimations} from './bottom-sheet-animations';
     'class': 'mat-bottom-sheet-container',
     'tabindex': '-1',
     '[attr.role]': '_config.role',
-    '[attr.aria-modal]': '_config.isModal',
+    '[attr.aria-modal]': '_config.ariaModal',
     '[attr.aria-label]': '_config.ariaLabel',
     '[@state]': '_animationState',
     '(@state.start)': '_onAnimationStart($event)',

src/material/bottom-sheet/bottom-sheet.spec.ts

@@ -156,6 +156,7 @@ describe('MatBottomSheet', () => {
 
     const containerElement = overlayContainerElement.querySelector('mat-bottom-sheet-container')!;
     expect(containerElement.getAttribute('role')).toBe('dialog');
+    expect(containerElement.getAttribute('aria-modal')).toBe('true');
   });
 
   it('should close a bottom sheet via the escape key', fakeAsync(() => {

tools/public_api_guard/material/bottom-sheet.md

@@ -66,6 +66,7 @@ export const matBottomSheetAnimations: {
 // @public
 export class MatBottomSheetConfig<D = any> {
     ariaLabel?: string | null;
+    ariaModal?: boolean;
     autoFocus?: AutoFocusTarget | string | boolean;
     backdropClass?: string;
     closeOnNavigation?: boolean;