Data table descriptions are incorrect on iOS 13 and later

[NickEntin]

The accessibility description for elements in a data table appears to have subtly changed on iOS 13. The differences can be seen in the following tests:

testDataTable

• The final element now reads as "B5: Value. Row 5. Column 2. Dimmed. Button. Heading. Link. Adjustable. Image. Search Field. 5 of 1." / "Hint"

The most obvious change here is that the accessibilityValue comes before the row and column numbers. I'm not sure where the "5 of 1" came from.

testDataTableWithHeaders

• The first element in the table now reads as "B1: B1 Value. C1: C1 Value. A2: A2 Value. A3: A3 Value. A1: A1 Value. Row Header. Column Header. Row 1. Column 1."
• The addition of the "Row Header" label is applied to all cells the first three columns.
• The addition of the "Column Header" label is applied to all cells the first three rows.
• The movement of accessibilityValue from before is applied to all cells.

testDataTableWithUndefinedRows

• The first element in the table now reads as "A2: A2 Value. A3: A3 Value. A1: A1 Value. Column Header. Row -9223372036854775808. Column 1"
• The second element in the table now reads as "B2: B2 Value. B3: B3 Value. B1: B1 Value. Column Header. Column 2."
• The addition of the "Column Header" label is applied to all cells the first three rows.
• The movement of accessibilityValue from before is applied to all cells.

I think the row number in the first cell is coming from an overflow of NSNotFound + 1. This feels like a regression in VoiceOver, but we should try to match the behavior of VoiceOver in our descriptions as close as possible.

[NickEntin]

Marking this as P1: High Priority based on the missing "Row/Column Header" labels. If we can fix the header labels, I think the rest will be a P2.

[NickEntin]

These changes will apply to iOS 14 as well, potentially with a few more additions.