add source.Location + reorient Resolvers to use it

Signed-off-by: Alex Goodman <alex.goodman@anchore.com>

syft/source/location.go

@@ -0,0 +1,46 @@
+package source
+
+import (
+	"github.com/anchore/syft/internal/log"
+
+	"github.com/anchore/stereoscope/pkg/file"
+	"github.com/anchore/stereoscope/pkg/image"
+)
+
+type Location struct {
+	Path       string `json:"path"`
+	LayerIndex uint   `json:"layerIndex"`
+	LayerID    string `json:"layerID"`
+	ref        file.Reference
+}
+
+func newLocation(path string) Location {
+	return Location{
+		Path: path,
+	}
+}
+
+func newLocationFromRef(ref file.Reference) Location {
+	return Location{
+		Path: string(ref.Path),
+		ref:  ref,
+	}
+}
+
+func newLocationFromImage(ref file.Reference, img *image.Image) Location {
+	entry, err := img.FileCatalog.Get(ref)
+	if err != nil {
+		log.Warnf("unable to find file catalog entry for ref=%+v", ref)
+		return Location{
+			Path: string(ref.Path),
+			ref:  ref,
+		}
+	}
+
+	return Location{
+		Path:       string(ref.Path),
+		LayerIndex: entry.Source.Metadata.Index,
+		LayerID:    entry.Source.Metadata.Digest,
+		ref:        ref,
+	}
+}