Accessibility improvements for Calendar

[MilenaCh]

• Update aria-label text of the navigation arrows to be more meaningful.
• Add meaningful aria-label to fast navigation button.
• Add aria-label template for date cells in the calendar. The developer will be able to manipulate what part of the date to add as aria-label.
• Remove aria-multiselectable="true" attribute as it is not allowed on the Calendar container (in selectable: "multiple" scenario).