The Parent method will no longer make sense with forthcoming Merge and
Diff support as refs will become capable of having multiple parents. It
was also only ever used externally to get the full chain of refs for
each layer in the ref's chain.
The newly added LayerChain method replaces Parents with a method that
just returns a slice of refs for each layer in the ref's chain. This
will work more seamlessly with Merge and Diff (in which case it returns
the "flattened" ancestors of the ref) in addition to being a bit easier
to use for the exiting cases anyways.
Signed-off-by: Erik Sipsma <erik@sipsma.dev>
03ed0548ef