[multi-select-combo-box] Clear button does not work on iOS

[web-padawan]

Description

When clear-button-visible is set, tapping the button does not work.

msc-clear.mp4

Expected outcome

Expected clear button to clear on touchend, like it works in the regular vaadin-combo-box:

web-components/packages/combo-box/src/vaadin-combo-box-mixin.js

Lines 1291 to 1297 in 61d8f07

	_onTouchend(event) {
	if (!this.clearElement || event.composedPath()[0] !== this.clearElement) {
	return;
	}
	event.preventDefault();
	this._clear();

Minimal reproducible example

Check the example in the dev page.

Steps to reproduce

1. Select some items
2. Tap the "clear" button

Environment

Vaadin version(s): 23.2 alpha, 23.1

Browsers

Issue is not browser related

[web-padawan]

I had to do some research in order to justify the need for this touchend prevention. Here are my observations:

1. The touchend listener was originally added by Set clear button not opening the overlay vaadin-combo-box#620
2. Then it was changed in Fix toggling/clearing bug of <vaadin-combo-box-light> on mobile vaadin-combo-box#648
3. Similar PR for date-picker: Set clear button not opening the overlay vaadin-date-picker#515

The actual reason for such behavior, as far as I remember, was to make it possible to clear the vaadin-combo-box on mobile device without focusing the input element (which we now do on clear button mousedown, see #2619).

Here is how clear button works for existing components (tested on desktop and with iOS Simulator):

component	Desktop	iOS Simulator
vaadin-combo-box	Focus	Don't focus
vaadin-time-picker	Focus	Don't focus
vaadin-date-picker	Don't focus	Don't focus
vaadin-text-field	Focus	Focus

I will create a separate issue to discuss whether we should align this behavior.
Until then, the solution would be to add touchend listener to vaadin-multi-select-combo-box.