[#477] metabase: Move MergeSplitInfo to storage/util pkg

This function already reused in different storage engine parts
so it makes sense to keep it in separate package.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/local_object_storage/util/splitinfo.go

@@ -0,0 +1,21 @@
+package util
+
+import (
+	objectSDK "github.com/nspcc-dev/neofs-api-go/pkg/object"
+)
+
+// MergeSplitInfo ignores conflicts and rewrites `to` with non empty values
+// from `from`.
+func MergeSplitInfo(from, to *objectSDK.SplitInfo) *objectSDK.SplitInfo {
+	to.SetSplitID(from.SplitID()) // overwrite SplitID and ignore conflicts
+
+	if lp := from.LastPart(); lp != nil {
+		to.SetLastPart(lp)
+	}
+
+	if link := from.Link(); link != nil {
+		to.SetLink(link)
+	}
+
+	return to
+}