HP-2651: Use billing registry in Price creation UI to render unit dropdown (#106)

* HP-2651: Use billing registry in Price creation UI to render unit dropdown

* HP-2651: added FractionUnit::equals() method

Author: VadymHrechukha

src/product/Domain/Model/Unit/FractionUnitInterface.php

@@ -4,5 +4,9 @@
 
 interface FractionUnitInterface
 {
+    public function name(): string;
 
+    public function label(): string;
+
+    public function equals(FractionUnitInterface $other): bool;
 }