Provide a way to ask Atspi for its version

I would like to be able to ask Atspi for its version (e.g. 2.48.3) within Orca and without having to do any hacks.

Use case: Mike landed a fix related to collection (thanks!!), and I'd like to conditionally use it based on the version. That way, I don't have to bump dependencies.

I found atspi_accessible_get_atspi_version, but that's defined as:

 * Gets the AT-SPI IPC specification version supported by the application
 * pointed to by the #AtspiAccessible object.
 * Only works on application root objects.

Could we please have an atspi_get_version, @mgorse?

Related aside/question: The reported version is 2.1 for all the apps I've checked so far. Do I have any use for that information in terms of Orca? Who are the consumers of that value?