AST-1168 Rename Casacore get() functions
- Rename DPBuffer::getData() etc to DPBuffer::GetCasacoreData().
- Enable/Add DPBuffer::GetData() functions that return XTensor views.
- Use pointers from XTensor views (
getData().data()
etc is nowGetData().data()
). This change also partially tests that the XTensor views are correct.