Add test cases for user type operators with global using for directive

test/libsolidity/syntaxTests/using/override_user_type_operator_defined_as_global.sol

@@ -0,0 +1,24 @@
+==== Source: s1.sol ====
+type Int is int;
+using {add as +} for Int global;
+
+function add(Int, Int) pure returns (Int) {
+    return Int.wrap(3);
+}
+
+==== Source: s2.sol ====
+import "s1.sol";
+
+using {another_add as +} for Int;
+
+function another_add(Int, Int) pure returns (Int) {
+    return Int.wrap(3);
+}
+
+contract C {
+    function f() pure public {
+        Int.wrap(0) + Int.wrap(0);
+    }
+}
+// ----
+// TypeError 2271: (s2.sol:184-209): Operator + not compatible with types Int and Int. Multiple user-defined functions provided for this operator.

test/libsolidity/syntaxTests/using/user_type_operator_defined_as_global.sol

@@ -0,0 +1,15 @@
+==== Source: s1.sol ====
+type Int is int;
+using {add as +} for Int global;
+
+function add(Int, Int) pure returns (Int) {
+    return Int.wrap(3);
+}
+
+==== Source: s2.sol ====
+import "s1.sol";
+contract C {
+    function f() pure public {
+        Int.wrap(0) + Int.wrap(0);
+    }
+}