Add Mixed Geometry Column

[isVoid]

Description

This is an initial introduction of mixed geometry column.

A mixed geometry column is a specialization of arrow's dense union layout column. It doesn't allow arbitrary types defined for the column but is always strongly typed for all 6 commonly used geometry types in cuspatial: points, linestrings, polygons, multipoints, multilinestrings, multipolygons.

Type codes is also fixed to what's defined in cuspatial/types.hpp. The actual value of these can be retrieved by casting the enum type to mixed_geometry_type_t.

closes #1057

Checklist

• [x] I am familiar with the Contributing Guidelines.
• [x] New or existing tests cover these changes.
• [x] The documentation is up to date with these changes.