Add single asset vault (XLS-65d) (#5224)

- Specification: XRPLF/XRPL-Standards#239
- Amendment: `SingleAssetVault`
- Implements a vault feature used to store a fungible asset (XRP, IOU, or MPT, but not NFT) and to receive shares in the vault (an MPT) in exchange.
- A vault can be private or public.
- A private vault can use permissioned domains, subject to the `PermissionedDomains` amendment.
- Shares can be exchanged back into asset with `VaultWithdraw`.
- Permissions on the asset in the vault are transitively applied on shares in the vault.
- Issuer of the asset in the vault can clawback with `VaultClawback`.
- Extended `MPTokenIssuance` with `DomainID`, used by the permissioned domain on the vault shares.

Co-authored-by: John Freeman <jfreeman08@gmail.com>

include/xrpl/protocol/STNumber.h

@@ -63,6 +63,13 @@ public:
     void
     setValue(Number const& v);
 
+    STNumber&
+    operator=(Number const& rhs)
+    {
+        setValue(rhs);
+        return *this;
+    }
+
     bool
     isEquivalent(STBase const& t) const override;
     bool
@@ -83,6 +90,19 @@ private:
 std::ostream&
 operator<<(std::ostream& out, STNumber const& rhs);
 
+struct NumberParts
+{
+    std::uint64_t mantissa = 0;
+    int exponent = 0;
+    bool negative = false;
+};
+
+NumberParts
+partsFromString(std::string const& number);
+
+STNumber
+numberFromJson(SField const& field, Json::Value const& value);
+
 }  // namespace ripple
 
 #endif