fix(ui5-date-picker): adjust value help icon role (#5419)

The ui5-date-picker value help icon is still decorative, but now has role "button".
On desktop the value help icon should be hidden from the screen reader.
For mobile devices the icon is visible for the screen readers, in order to enable
explore by touch scenarios.

Fixes: #5378

Author: unazko

packages/main/src/DatePicker.hbs

@@ -31,6 +31,8 @@
 				name="{{openIconName}}"
 				tabindex="-1"
 				accessible-name="{{openIconTitle}}"
+				accessible-role="button"
+				aria-hidden="{{_ariaHidden}}"
 				show-tooltip
 				@click="{{togglePicker}}"
 				input-icon

packages/main/src/DatePicker.js

@@ -16,7 +16,7 @@ import {
 	isF4,
 	isEnter,
 } from "@ui5/webcomponents-base/dist/Keys.js";
-import { isPhone } from "@ui5/webcomponents-base/dist/Device.js";
+import { isPhone, isDesktop } from "@ui5/webcomponents-base/dist/Device.js";
 import "@ui5/webcomponents-icons/dist/appointment-2.js";
 import "@ui5/webcomponents-icons/dist/decline.js";
 import HasPopup from "./types/HasPopup.js";
@@ -705,6 +705,14 @@ class DatePicker extends DateComponentBase {
 		return false;
 	}
 
+	/**
+	 * Defines whether the value help icon is hidden
+	 * @private
+	 */
+	get _ariaHidden() {
+		return isDesktop();
+	}
+
 	async _respPopover() {
 		const staticAreaItem = await this.getStaticAreaItemDomRef();
 		return staticAreaItem.querySelector("[ui5-responsive-popover]");