AT-SPI: add "getRole"

[spectranaut]

We currently have getRoleName which wraps atspi_accessible_get_role_name. We should also have a getRole, which would wrap atspi_accessible_get_role.

In general, for functions that return a constant or enum, we convert the name of the constant or enum to a string. Such as the windows getAccRole and in linux getStates.

I wonder if we should instead return the constant or enum directly, and provide a utility for the user of the library to convert it into a readable string.. but that can be a future change.