feat(ui5-date-range): introduce new calendar date type

[didip1000]

Introducing ui5-date-range a CalendarDateRange element, similar to the CalendarDate elementui5-date.

A ui5-date-range has a startValue and an endValue which are strings marking the start and end dates of a calendar range.

BREAKING CHANGE: dates slot in a calendar now works with a ui5-date-range when selection-mode="Range"

Previously date ranges were declared as follows:

<ui5-calendar selection-mode="Range">
        <ui5-date value="Jan 20, 2021"></ui5-date>
        <ui5-date value="Jan 30, 2021"></ui5-date>
</ui5-calendar>

Now they are declared using a ui5-date-range:

<ui5-calendar selection-mode="Range">
	<ui5-date-range start-value="Jan 20, 2021" end-value="Jan 30, 2021"></ui5-date-range>
</ui5-calendar>

Related to: https://github.com/SAP/ui5-webcomponents/issues/8461

[vladitasev]

I did not checkout or test the change, but did a high-level review and looks good to me