chart2: fix memory leak due to cyclic reference in VAxisBase

The VAxisBase::m_xNumberFormatsSupplier refers to the ChartModel itself,
and apparently that is a cyclic reference.  Naively using the
ChartModel's m_xNumberFormatsSupplier in
ChartView::impl_createDiagramAndContent() because it will later be passed
to AxisHelper::getExplicitNumberFormatKeyForAxis(), which expects to be
able to convert it to a ChartModel.

Since passing around the ChartModel as an XNumberFormattingSupplier is
sort of un-intuitive anyway, refactor some methods to use XChartDocument
instead, and only create the VPolarAxis / VCartesianAxis with the
ChartModel's m_xNumberFormatsSupplier.

The drawback is that if ChartModel::attachNumberFormatsSupplier()
is called after ChartView::update() has created the axes, it may not
have an effect on them; not sure if that is a real or hypothetical
problem.

Change-Id: Ib5f0d5882b85adaf44f80e086f19178b3e64882f