fix(list-key-manager): prevent the default keyboard actions

[crisbeto]

Calls preventDefault when handling keyboard events in the ListKeyManager. This avoids the user scrolling the page when using the arrow keys to navigate.

Relates to #1999.

[jelbourn]

Instead of calling preventDefault in each case, you can do:

  onKeydown(event: KeyboardEvent): void {
    switch (event.keyCode) {
      case DOWN_ARROW:
        this.focusNextItem();
        break;
      case UP_ARROW:
        this.focusPreviousItem();
        break;
      case HOME:
        this.focusFirstItem();
        break;
      case END:
        this.focusLastItem();
        break;
      case TAB:
        this._tabOut.next(null);
        return;
      default: 
        return;
    }

    event.preventDefault();
  }

(see slider.ts for an example)

[crisbeto]

It's not supposed to be called when tabbing, though. I initially went with something similar but it broke the menu e2e tests.

[jelbourn]

That's why the tab case has a return
(it does need a comment to point that out, though)

[crisbeto]

Updated. Also added a unit test for tab, just in case.

[jelbourn]

R: @kara

[kara]

LGTM

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