QDateEdit shows day as number when format includes ddd or dddd

As a result of testing QTBUG-26847, it was found that QDateEdit will also temporarily display a short or long day name as its numerical value under the same circumstances as the aforementioned bug.

1. QDateEdit has the display format set to 'yyyy/MM/ddd' (or any format with a short or long day name)
2. The date value is edited to '31' (cycle through the days by holding the up key)
3. The focus is changed to month with Shift + Tab
4. The month value is edited to '2'
5. The date value shows '29' until cursor is moved or focus changed (or 291 if https://codereview.qt-project.org/#change,33204 is not applied)

The reason this happens is because QDateTimeParser doesn't distinguish between day names and numbers:

if (sectionType(i) & (DaySection|DayOfWeekSection)) {
   input.replace(sectionPos(i), sectionSize(i), loc.toString(day));
}

Attached is a patch (to go on top of the aforementioned change) which contains unit tests demonstrating the issue.