Autotest: Update textedit test using textFormat

TextEdit does not support the StyledText format, Text does.

Add an autotest to Text to check the line counts using
different text formats.

Task-number: QTBUG-31191

Change-Id: I4670f9155bea295ba85f410988d9636eac12842c
Reviewed-by: Andrew den Exter <andrew.den.exter@qinetic.com.au>
Reviewed-by: Liang Qi <liang.qi@digia.com>