This was forgotten when implementing QTBUG-73160, but suggested in
passing in QTBUG-64.
[ChangeLog][QtGui][QPolygon] Added toPolygonF().
Task-number: QTBUG-73160
Task-number: QTBUG-64
Change-Id: I9b33cf47a0d432aa842ab0f8337001c66e4ca41c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>