Create more semantic testcases from the feedback

semantic/array_creation_boolean.invalid.mj

+class Test {
+    public static void main(String[] args) {
+        int[] a = new int[false];
+    }
+}

semantic/array_creation_ident.invalid.mj

+class Test {
+    public static void main(String[] args) {
+        Test test = null;
+        int[] a = new int[test];
+    }
+}

semantic/array_creation_null.invalid.mj

+class Test {
+    public static void main(String[] args) {
+        int[] a = new int[null];
+    }
+}

semantic/call_method_on_assignment.java

+class Test {
+    public static void main(String[] args) {
+        Test test = null;
+        (test = new Test()).test();
+        (test = new Test()).test = 5;
+        (test.test()).test();
+
+        Test[] tests = null;
+        (tests = new Test[5])[0].test();
+        
+        new Test[5][0].test();
+    }
+
+    public Test test() {
+        return this;
+    }
+
+    public int test;
+}

semantic/call_method_on_undefined_type.invalid.mj

+class Test {
+    public static void main(String[] args) {
+        Foo foo = new Foo();
+        foo.foo();
+        foo.foo = 123;
+        foo.main(null);
+    }
+}

semantic/compare_system.invalid.java

+class Test {
+    public static void main(String[] args) {
+        boolean test = System == System;
+    }
+}

semantic/compare_system_in.invalid.java

+class Test {
+    public static void main(String[] args) {
+        boolean test = System.in == System.in;
+    }
+}

semantic/compare_system_null.invalid.java

+class Test {
+    public static void main(String[] args) {
+        boolean test = System.out == null;
+    }
+}

semantic/compare_system_out.invalid.java

+class Test {
+    public static void main(String[] args) {
+        boolean test = System.out == System.out;
+    }
+}

semantic/invalid_compare_null_int.invalid.mj

+class Test {
+    public static void main(String[] args) {
+        boolean b = null && 2;
+    }
+}

semantic/missing_return_value.invalid.mj

+class Test {
+    public static void main(String[] args) {
+    }
+    public int foo() {
+        return;
+    }
+}