This is a subtask of tdf#165742: Chartex charts are lost on input from OOXML
and re-export.
Build out the narrowest parsing path down to ChartType for funnel charts.
No other data or parameters are supported at this point other than the
chart type. This is a step towards more extensive support for I/O of chartex
charts to/from OOXML.
Change-Id: If33f4320c373262de19a7b0b31d28ce8f1de29e8
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/183463
Tested-by: Jenkins
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>