fix(material/tabs): add aria-hidden to inactive tabs (#27742)

Make accessibility fix for Tabs component. Add `aria-hidden="true"` to
inactive tab panels. Fix issue where chromevox would read the names of
inactive tab panels when navigating past the active tab panel (#27741).
Fix this by adding `aria-hidden="true"` to inactive tab panels to
exclude them from the a11y tree.

I believe what was happening is that the inactive tab panels had an
aria-labelled by references that pointed to the tab header. Existing
behavior seems to be that Chromevox was following the aria-labelledby
references and announcing the labels of the inactive tabs. With this
commit applied, Chromevox no longer reads panels of inactive tabs.

Fix #27741

src/material/tabs/tab-group.html

@@ -58,6 +58,7 @@
                [id]="_getTabContentId(i)"
                [attr.tabindex]="(contentTabIndex != null && selectedIndex === i) ? contentTabIndex : null"
                [attr.aria-labelledby]="_getTabLabelId(i)"
+               [attr.aria-hidden]="selectedIndex !== i"
                [class.mat-mdc-tab-body-active]="selectedIndex === i"
                [ngClass]="tab.bodyClass"
                [content]="tab.content!"

src/material/tabs/tab-group.spec.ts

@@ -441,6 +441,25 @@ describe('MDC-based MatTabGroup', () => {
     });
   });
 
+  describe('aria labelling of tab panels', () => {
+    let fixture: ComponentFixture<BindedTabsTestApp>;
+    let tabPanels: HTMLElement[];
+
+    beforeEach(fakeAsync(() => {
+      fixture = TestBed.createComponent(BindedTabsTestApp);
+      fixture.detectChanges();
+      tick();
+      tabPanels = Array.from(fixture.nativeElement.querySelectorAll('.mat-mdc-tab-body'));
+    }));
+
+    it('should set `aria-hidden="true"` on inactive tab panels', () => {
+      fixture.detectChanges();
+
+      expect(tabPanels[0].getAttribute('aria-hidden')).not.toBe('true');
+      expect(tabPanels[1].getAttribute('aria-hidden')).toBe('true');
+    });
+  });
+
   describe('disable tabs', () => {
     let fixture: ComponentFixture<DisabledTabsTestApp>;