QTextFormat::font{Weight,PointSize}() etc. return the font trait explicitly
set on the QTextFormat, while QTextFormat::font() returns font which also
uses the QTextDocument::defaultFont() as a default for any font traits not
explicitly set on the QTextFormat. Accessibility support for text attributes
used the former, which was wrong; this commit fixes it to use the latter.
Also includes tests to verify the fix.
Change-Id: Iab7f2be1b68adaad847d1f29c9e5af2195416035
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@theqtcompany.com>