Introduce MPT support (XLS-33d): (#5143)

Amendment:
- MPTokensV1

New Transactions:
- MPTokenIssuanceCreate
- MPTokenIssuanceDestroy
- MPTokenIssuanceSet
- MPTokenAuthorize

Modified Transactions:
- Payment
- Clawback

New Objects:
- MPTokenIssuance
- MPToken

API updates:
- ledger_entry
- account_objects
- ledger_data

Other:
- Add += and -= operators to ValueProxy

Read full spec: https://github.com/XRPLF/XRPL-Standards/tree/master/XLS-0033d-multi-purpose-tokens

---------
Co-authored-by: Shawn Xie <shawnxie920@gmail.com>
Co-authored-by: Howard Hinnant <howard.hinnant@gmail.com>
Co-authored-by: Ed Hennis <ed@ripple.com>
Co-authored-by: John Freeman <jfreeman08@gmail.com>

include/xrpl/protocol/AmountConversions.h

@@ -33,13 +33,7 @@ toSTAmount(IOUAmount const& iou, Issue const& iss)
 {
     bool const isNeg = iou.signum() < 0;
     std::uint64_t const umant = isNeg ? -iou.mantissa() : iou.mantissa();
-    return STAmount(
-        iss,
-        umant,
-        iou.exponent(),
-        /*native*/ false,
-        isNeg,
-        STAmount::unchecked());
+    return STAmount(iss, umant, iou.exponent(), isNeg, STAmount::unchecked());
 }
 
 inline STAmount