Calendar Accessibility: Prevent VoiceOver Calendar Scrollback

[joshheald]

Fixes #17760

Description

Previously, when moving VoiceOver focus from the next button to the Date Cells on the Schedule Post popover, the calendar would scroll back to 1 Jan 1951.

This automated scrollback is a probably-intentional part of UICollectionView (to enable VoiceOver to read everything in a collection view) but it is not appropriate in its use here as a calendar.

This change prevents that automated scrollback, and only makes any change when the relevant accessibility features are in use.

The same issue happened sporadically on the year view calendar; I wasn't able to find repro steps for that, but this change should improve the behaviour there as well.

To test:

On the Schedule Post screen:

1. Open the calendar with VoiceOver enabled
2. Swipe left repeatedly until you get to a date cell
3. Observe that the first date cell you reach is the first visible cell, rather than 1 Jan 1951

Screenshots

VoiceOver.calendar.scrollback.fixed.mp4

Regression Notes

1. Potential unintended areas of impact
   General use of the calendar should be unaffected; the UIAccessibility.isVoiceOverRunning check which gates the changes will prevent issues when VoiceOver is not in use.
   Anywhere which scrolls the calendar automatically should be tested carefully. The Next/Previous Month buttons are examples of those, and other possibilities are layout changes, e.g. portrait/landscape, iPad size class changes.

Note that even without these changes, the calendar does not respond well to layout changes (the months stop fitting on the screen).

Also note, I do not have a physical iPad to test these changes on, so they have only been tested on a physical phone and an iPad simulator. To test on an iPad simulator, I had to change the condition in CalendarCollectionView.shouldPreventAccessibilityFocusScrollback(for:) to be if UIAccessibility.isVoiceOverRunning || UIDevice.isPad() and use the Accessibility Inspector to move between elements, as the Inspector does not count as voiceover.

The calendar is used both on the Activity Log date filter, and the Schedule Post date selector.

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   Extensive VoiceOver and Switch Control use of the calendar

3. What automated tests I added (or what prevented me from doing so)
   None

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding unit tests for my changes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

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[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[momo-ozawa]

Works as described! Tested on a real iPad. :)