Make as_component_get_sort_score public

[davidmhewitt]

Fixes #269

It turns out that this is a guint rather than a custom type, so this works out perfectly in the vapi.

I know you wanted to have a bit more of a think about this in terms of whether this score is suitable for comparing components in disparate pools and whether this is the right approach, but I feel happier that I've done a tiny bit of the leg work 😝

[davidmhewitt]

@ximion Sorry to chase you, but have you had any chance to think about this? Is there anything else I can do to help out with this?

[ximion]

It's a custom type because it's typedef'ed, but the sort score return value happens to be a guint.
I will make this public API, but I'll go with a different patch than this one because I will also have to adjust some documentation texts (and I would rather do this in one commit). So, the next release will likely have this.
Thank you for creating this PR though!