Adding field to `ocamllsp/typeEnclosing` to indicate value vs. module type

[ddickstein]

The result of ocamllsp/typeEnclosing currently provides no explicit indication about whether the type returned is a value type or a module type. In some cases it can be other things too, such as a type definition (when the type of a type definition is requested). It would be helpful to have an explicit field indicating which sort of type is being returned to ensure proper rendering.