Custom Calendar: accessibility issues

Our custom calendar has accessibility issues. Both when scheduling a post and when selecting a date range from Activity Log:

• Unavailable (future) dates are not announced as unavailable.
• Dates of the week ( S M T W T F S) are incorrectly announced: eg. F is announced as “half-F, night sky”
• While scrolling up and down announcements say “Page 138” which is not super helpful. Maybe we can announce something else, like the month visible on the screen?
• Month name in date picker cuts off when using large font

How to reproduce

1. Open Activity Log for any site with available filters
2. Using Voice Over, test the aforementioned items

Prioritised tasks from investigation

• #17760
• #17780
• Calendar accessibility: Prevent hidden Activity Type chip from grabbing VoiceOver focus when using the Activity Log date filter
• Calendar accessibility: Add heading trait to month headings for navigation
• Calendar accessibility: Make month headings show at larger dynamic type sizes on Schedule Post
• Calendar accessibility: Make day numbers show at larger dynamic type sizes on Schedule Post
• Calendar accessibility: Make month headings show at larger dynamic type sizes on Activity Log
• Calendar accessibility: Make day numbers show at larger dynamic type sizes on Activity Log
• Calendar accessibility: Announce future dates as unavailable for selection when using the Activity Log filter
• Calendar accessibility: Announce selected dates as selected
• Calendar accessibility: Announce weekday for selectable dates, instead of as headings
• Calendar accessibility: Announce current selection as a date range
• Calendar accessibility: Give descriptive accessibilityLabels to the previous/next month buttons on Schedule Post
• Calendar accessibility: Announce month(s)/year(s) on screen when scrolling, not page numbers

Start by reproducing the remaining calendar issues in Activity Log and Schedule Post with VoiceOver, using the unchecked tasks as the scope. Inspect the custom calendar accessibility behavior for hidden Activity Type focus, dynamic type, future-date announcements, and scrolling; done means the remaining listed behaviors work correctly without the reported announcements or clipping.