This commit enables parsing the doc_value parameter
in GeoShapeFieldMapper and ShapeFieldMapper when
the xpack spatial module is loaded. Licensing is Basic+.

This commit introduces the following behavior:

* doc_values defaults to true for GeoShapeFieldMapper and ShapeFieldMapper when the Spatial XPack module is available
* doc_values are not supported for geo_shape PrefixTree indexing (same behavior as before)
* doc_values defaults to false for GeoShapeFieldMapper and ShapeFieldMapper when the Spatial XPack module is not available (e.g., OSS)
* when doc_values are set in OSS, a MapperParsingException is thrown (same behavior as before)

This PR adds support for the `doc_values` field mapping parameter.

`false` is currently the only supported value to explicitly
set, and is also the default.