need way to calculate a source package's current NEVR after applying TOML (overlays, etc.)

[reubeno]

This is critical to getting %autorelease working correctly.

Related to #25

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Imported on behalf of @ddstreet

[dmcilvaney]

Experiments here: https://github.com/dmcilvaney/azure-linux-dev-tools/tree/damcilva/expand_component_query_nevr