fix(popover-edit): unable to close focus content using the keyboard (#18945)

The popover edit shows some content either when a cell is hovered or when it's focused, but the problem is that keyboard users don't have a way of closing the focus content without moving focus completely out of the table, because tabbing again usually lands on a different cell. These changes allow for the focus content to be removed by pressing the Escape key.

(cherry picked from commit 17f8e94)

Author: crisbeto

src/cdk-experimental/popover-edit/popover-edit.spec.ts

@@ -441,6 +441,21 @@ describe('CDK Popover Edit', () => {
           expect(component.hoverContentStateForRow(4)).toBe(HoverContentState.FOCUSABLE);
         }));
 
+        it('should close the focus content when pressing escape', fakeAsync(() => {
+          expect(component.hoverContentStateForRow(2)).toBe(HoverContentState.OFF);
+
+          component.focusEditCell(2);
+          tick(1);
+
+          expect(component.hoverContentStateForRow(2)).toBe(HoverContentState.ON);
+
+          const event = new KeyboardEvent('keydown', {bubbles: true, key: 'Escape'});
+          component.getEditCell(2).dispatchEvent(event);
+          tick(1);
+
+          expect(component.hoverContentStateForRow(2)).toBe(HoverContentState.OFF);
+        }));
+
         it('shows hover content for the editing row and makes the rows above and below ' +
             'focusable unless focus is in a different table row in which case it takes priority',
             fakeAsync(() => {

src/cdk-experimental/popover-edit/table-directives.ts

@@ -104,21 +104,25 @@ export class CdkEditable implements AfterViewInit, OnDestroy {
 
       // Track focus within the table to hide/show/make focusable hover content.
       fromEventPattern<FocusEvent>(
-          (handler) => element.addEventListener('focus', handler, true),
-          (handler) => element.removeEventListener('focus', handler, true)
+          handler => element.addEventListener('focus', handler, true),
+          handler => element.removeEventListener('focus', handler, true)
           ).pipe(
               takeUntil(this.destroyed),
               toClosest(ROW_SELECTOR),
               share(),
               ).subscribe(this.editEventDispatcher.focused);
-      fromEventPattern<FocusEvent>(
-          (handler) => element.addEventListener('blur', handler, true),
-          (handler) => element.removeEventListener('blur', handler, true)
-          ).pipe(
-              takeUntil(this.destroyed),
-              mapTo(null),
-              share(),
-              ).subscribe(this.editEventDispatcher.focused);
+
+      merge(
+        fromEventPattern<FocusEvent>(
+          handler => element.addEventListener('blur', handler, true),
+          handler => element.removeEventListener('blur', handler, true)
+        ),
+        fromEvent<KeyboardEvent>(element, 'keydown').pipe(filter(event => event.key === 'Escape'))
+      ).pipe(
+        takeUntil(this.destroyed),
+        mapTo(null),
+        share(),
+      ).subscribe(this.editEventDispatcher.focused);
 
       // Keep track of rows within the table. This is used to know which rows with hover content
       // are first or last in the table. They are kept focusable in case focus enters from above