Autocomplete closes when scrolling on a touch device

[csidorenko]

Steps to reproduce:

1. Open https://material.angular.io/components/autocomplete/overview in any touch device
2. Use the example on the page, tap to show autocomplete
3. If it was a longer list or you're viewing on a small device you would want to scroll to see the rest of the list. Scroll with touch.
4. On touchend the autocomplete closes

Expected Behavior

It is the intended behavior according to the code in autcomplete.es5.js L:601

return merge(fromEvent(this._document, 'click'), fromEvent(this._document, 'touchend'))`
    .pipe(filter(function (event) {
            /** @type {?} */
            var clickTarget = (/** @type {?} */ (event.target));
            /** @type {?} */
            var formField = _this._formField ?
                _this._formField._elementRef.nativeElement : null;
            return _this._overlayAttached &&
                clickTarget !== _this._element.nativeElement &&
                (!formField || !formField.contains(clickTarget)) &&
                (!!_this._overlayRef && !_this._overlayRef.overlayElement.contains(clickTarget));
        }));

The menu closes on touchend but I think it's a bug because it's normal to expect users to scroll on a mobile device to see the rest of the list. I think the fromEvent(this._document, 'touchend') should be removed or the code changed to allow scrolling

Environment

• Angular: 7.2.13
• CDK/Material: 7.3.7
• Browser(s): All browsers on a touch device
• Operating System (e.g. Windows, macOS, Ubuntu): All operating systems that support touch