Add cimfs differ and snapshotter

Details about CimFs project are discussed in #8346

Signed-off-by: Amit Barve <ambarve@microsoft.com>

vendor/github.com/Microsoft/hcsshim/internal/hcs/schema2/layer.go

@@ -9,6 +9,13 @@
 
 package hcsschema
 
+type FileSystemFilterType string
+
+const (
+	UnionFS FileSystemFilterType = "UnionFS"
+	WCIFS   FileSystemFilterType = "WCIFS"
+)
+
 type Layer struct {
 	Id string `json:"Id,omitempty"`