Introduce address(...).code

test/libsolidity/semanticTests/various/address_code.sol

@@ -0,0 +1,22 @@
+contract C {
+    bytes public initCode;
+
+    constructor() {
+        // This should catch problems, but lets also test the case the optimiser is buggy.
+        assert(address(this).code.length == 0);
+        initCode = address(this).code;
+    }
+
+    // To avoid dependency on exact length.
+    function f() public view returns (bool) { return address(this).code.length > 400; }
+    function g() public view returns (uint) { return address(0).code.length; }
+    function h() public view returns (uint) { return address(1).code.length; }
+}
+// ====
+// compileViaYul: false
+// ----
+// constructor() ->
+// initCode() -> 0x20, 0
+// f() -> true
+// g() -> 0
+// h() -> 0