generialize cmp candidate from Pair to Enum

src/core/Enum.pm

@@ -42,3 +42,6 @@ multi sub infix:<eqv>(Enum:D $a, Enum:D $b) {
     $a.WHAT === $b.WHAT && $a.key eqv $b.key && $a.value eqv $b.value
 }
 
+multi infix:<cmp>(Enum:D \$a, Enum:D \$b) {
+    ($a.key cmp $b.key) || ($a.value cmp $b.value)
+}

src/core/Pair.pm

@@ -13,7 +13,3 @@ my class Pair is Enum {
 sub infix:«=>»($key, Mu $value) { 
     Pair.new(:key($key), :value($value))
 }
-
-multi infix:<cmp>(Pair:D \$a, Pair:D \$b) {
-    ($a.key cmp $b.key) || ($a.value cmp $b.value)
-}