XDR definitions for Soroban constructor support. (#202)

Stellar-transaction.x

@@ -476,7 +476,8 @@ enum HostFunctionType
 {
     HOST_FUNCTION_TYPE_INVOKE_CONTRACT = 0,
     HOST_FUNCTION_TYPE_CREATE_CONTRACT = 1,
-    HOST_FUNCTION_TYPE_UPLOAD_CONTRACT_WASM = 2
+    HOST_FUNCTION_TYPE_UPLOAD_CONTRACT_WASM = 2,
+    HOST_FUNCTION_TYPE_CREATE_CONTRACT_V2 = 3
 };
 
 enum ContractIDPreimageType
@@ -503,6 +504,14 @@ struct CreateContractArgs
     ContractExecutable executable;
 };
 
+struct CreateContractArgsV2
+{
+    ContractIDPreimage contractIDPreimage;
+    ContractExecutable executable;
+    // Arguments of the contract's constructor.
+    SCVal constructorArgs<>;
+};
+
 struct InvokeContractArgs {
     SCAddress contractAddress;
     SCSymbol functionName;
@@ -517,20 +526,29 @@ case HOST_FUNCTION_TYPE_CREATE_CONTRACT:
     CreateContractArgs createContract;
 case HOST_FUNCTION_TYPE_UPLOAD_CONTRACT_WASM:
     opaque wasm<>;
+case HOST_FUNCTION_TYPE_CREATE_CONTRACT_V2:
+    CreateContractArgsV2 createContractV2;
 };
 
 enum SorobanAuthorizedFunctionType
 {
     SOROBAN_AUTHORIZED_FUNCTION_TYPE_CONTRACT_FN = 0,
-    SOROBAN_AUTHORIZED_FUNCTION_TYPE_CREATE_CONTRACT_HOST_FN = 1
+    SOROBAN_AUTHORIZED_FUNCTION_TYPE_CREATE_CONTRACT_HOST_FN = 1,
+    SOROBAN_AUTHORIZED_FUNCTION_TYPE_CREATE_CONTRACT_V2_HOST_FN = 2
 };
 
 union SorobanAuthorizedFunction switch (SorobanAuthorizedFunctionType type)
 {
 case SOROBAN_AUTHORIZED_FUNCTION_TYPE_CONTRACT_FN:
     InvokeContractArgs contractFn;
+// This variant of auth payload for creating new contract instances is no
+// longer accepted after protocol 22.
 case SOROBAN_AUTHORIZED_FUNCTION_TYPE_CREATE_CONTRACT_HOST_FN:
     CreateContractArgs createContractHostFn;
+// This variant of auth payload for creating new contract instances
+// is only accepted in and after protocol 22.
+case SOROBAN_AUTHORIZED_FUNCTION_TYPE_CREATE_CONTRACT_V2_HOST_FN:
+    CreateContractArgsV2 createContractV2HostFn;
 };
 
 struct SorobanAuthorizedInvocation