When the default format has letter and word spacing set then these
should be exported in the HTML's body tag. This also adds support
for the reading of letter-spacing and word-spacing set too, so that
the same html outputted can be read back in.
Fixes: QTBUG-83718
Change-Id: Ic4afca21eb05efb779dbf99c6b3c13373e851f15
Pick-to: 5.15
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>