Add test cases for field access from static contexts

semantic/field_access_from_static_context.invalid.mj

+class FieldAccessStatic {
+    public int nonStatic;
+
+    public static void main(String[] args) {
+        nonStatic = 42;
+    }
+}

semantic/field_access_on_class_identifier.invalid.mj

+class FieldAccess {
+    public int field;
+
+    public static void main(String[] args) {
+        new FieldAccess().accessField();
+    }
+
+    public void accessField() {
+        int i = FieldAccess.field;
+    }
+}