Rename spatial-data.md to spatial-vector.md

Major spatial features cover different spatial data types and their methods, such as:

• Vector data (currently described in spatial-data.md)
• Raster data (separate skills document planned)
• LRS (separate skills document wip)
• 3D data (separate skills document planned)

Hence, it makes sense to have "spatial" as file name prefix plus an identifier for the type of spatial data. Since it is not about data only but also about operators, functions, domain specific indexing, and so on, "data" will be removed from the file name.