Add Scale to SingleAssetVault (#5652)

* Add and Scale to VaultCreate
* Add round-trip calculation to VaultDeposit VaultWithdraw and VaultClawback
* Implement Number::truncate() for VaultClawback
* Add rounding to DepositWithdraw
* Disallow zero shares withdraw or deposit with tecPRECISION_LOSS
* Return tecPATH_DRY on overflow when converting shares/assets
* Remove empty shares MPToken in clawback or withdraw (except for vault owner)
* Implicitly create shares MPToken for vault owner in VaultCreate
* Review feedback: defensive checks in shares/assets calculations

---------

Co-authored-by: Ed Hennis <ed@ripple.com>

include/xrpl/basics/Number.h

@@ -150,6 +150,24 @@ public:
         return (mantissa_ < 0) ? -1 : (mantissa_ ? 1 : 0);
     }
 
+    Number
+    truncate() const noexcept
+    {
+        if (exponent_ >= 0 || mantissa_ == 0)
+            return *this;
+
+        Number ret = *this;
+        while (ret.exponent_ < 0 && ret.mantissa_ != 0)
+        {
+            ret.exponent_ += 1;
+            ret.mantissa_ /= rep(10);
+        }
+        // We are guaranteed that normalize() will never throw an exception
+        // because exponent is either negative or zero at this point.
+        ret.normalize();
+        return ret;
+    }
+
     friend constexpr bool
     operator>(Number const& x, Number const& y) noexcept
     {