Added an abi function test for UserDefinedValueType

A test to see if `abi.encode*(..., (CustomType))` and `abi.decode(..., (CustomType))` works as
intended.

test/libsolidity/semanticTests/userDefinedValueType/abicodec.sol

@@ -0,0 +1,36 @@
+// A test to see if `abi.encodeWithSelector(..., (CustomType))` works as intended.
+contract C {
+    type MyInt is int;
+    function f(MyInt x) external returns(MyInt a, MyInt b, MyInt c, MyInt d) {
+        a = MyInt.wrap(-1);
+        b = MyInt.wrap(0);
+        c = MyInt.wrap(1);
+        d = x;
+    }
+    function g() external returns(bool) {
+        (bool success1, bytes memory ret1) =  address(this).call(abi.encodeWithSelector(this.f.selector, MyInt.wrap(5)));
+        assert(success1);
+
+        (MyInt a1, MyInt b1, MyInt c1, MyInt d1) = abi.decode(ret1, (MyInt, MyInt, MyInt, MyInt));
+        assert(MyInt.unwrap(a1) == -1);
+        assert(MyInt.unwrap(b1) == 0);
+        assert(MyInt.unwrap(c1) == 1);
+        assert(MyInt.unwrap(d1) == 5);
+
+        (bool success2, bytes memory ret2) = address(this).call(abi.encodeWithSelector(this.f.selector, int(-5)));
+        assert(success2);
+
+        (int a2, int b2, int c2, int d2) = abi.decode(ret2, (int, int, int, int));
+        assert(a2 == -1);
+        assert(b2 == 0);
+        assert(c2 == 1);
+        assert(d2 == -5);
+
+        return true;
+    }
+}
+// ====
+// compileViaYul: also
+// EVMVersion: >=byzantium
+// ----
+// g() -> true