Fix token comparison in Payment (#5172)

* Checks only Currency or MPT Issuance ID part of the Asset object.
* Resolves temREDUNDANT regression detected in testing.

include/xrpl/protocol/Asset.h

@@ -97,6 +97,12 @@ public:
 
     friend constexpr bool
     operator==(Currency const& lhs, Asset const& rhs);
+
+    /** Return true if both assets refer to the same currency (regardless of
+     * issuer) or MPT issuance. Otherwise return false.
+     */
+    friend constexpr bool
+    equalTokens(Asset const& lhs, Asset const& rhs);
 };
 
 template <ValidIssueType TIss>
@@ -157,6 +163,26 @@ operator==(Currency const& lhs, Asset const& rhs)
     return rhs.holds<Issue>() && rhs.get<Issue>().currency == lhs;
 }
 
+constexpr bool
+equalTokens(Asset const& lhs, Asset const& rhs)
+{
+    return std::visit(
+        [&]<typename TLhs, typename TRhs>(
+            TLhs const& issLhs, TRhs const& issRhs) {
+            if constexpr (
+                std::is_same_v<TLhs, Issue> && std::is_same_v<TRhs, Issue>)
+                return issLhs.currency == issRhs.currency;
+            else if constexpr (
+                std::is_same_v<TLhs, MPTIssue> &&
+                std::is_same_v<TRhs, MPTIssue>)
+                return issLhs.getMptID() == issRhs.getMptID();
+            else
+                return false;
+        },
+        lhs.issue_,
+        rhs.issue_);
+}
+
 inline bool
 isXRP(Asset const& asset)
 {
@@ -172,6 +198,9 @@ validJSONAsset(Json::Value const& jv);
 Asset
 assetFromJson(Json::Value const& jv);
 
+Json::Value
+to_json(Asset const& asset);
+
 }  // namespace ripple
 
 #endif  // RIPPLE_PROTOCOL_ASSET_H_INCLUDED