Refactor vendor snapshot to use LinkableInterface.

Refactors the vendor snapshot support to use the LinkableInterface
so that support can be extended to Rust. This CL does not add
vendor snapshot support for Rust; that is left for a follow-on CL.

Bug: 184042776
Test: m nothing
Change-Id: Id0c4970ca00053484a52677d182153cbc454c301