Add test for interface code generation

tests/code_generation/TEST_generated_code.sol

@@ -0,0 +1,24 @@
+interface ITestContract {
+    event NoParams();
+    event Anonymous();
+    event OneParam(address);
+    event OneParamIndexed(address);
+    error ErrorWithEnum(uint8);
+    error ErrorSimple();
+    error ErrorWithArgs(uint256, uint256);
+    error ErrorWithStruct(uint256);
+    enum SomeEnum { ONE, TWO, THREE }
+    struct St {
+        uint256 v;
+    }
+    function stateA() external returns (uint256);
+    function owner() external returns (address);
+    function structs(address,uint256) external returns (uint256);
+    function err0() external;
+    function err1() external;
+    function err2(uint256,uint256) external;
+    function newSt(uint256) external returns (uint256);
+    function getSt(uint256) external view returns (uint256);
+    function removeSt(uint256) external;
+}
+