C++: Add test for implicit this

cpp/ql/test/library-tests/variables/this/this.cpp

@@ -0,0 +1,9 @@
+class TestImplicitThis
+{
+public:
+    int field;
+
+    int get() const {
+        return field + this->field + get() + this->get();
+    }
+};

cpp/ql/test/library-tests/variables/this/this.expected

@@ -0,0 +1,2 @@
+| this.cpp:7:16:7:20 | this |
+| this.cpp:7:38:7:40 | this |

cpp/ql/test/library-tests/variables/this/this.ql

@@ -0,0 +1,5 @@
+import cpp
+
+from ThisExpr te
+where te.isCompilerGenerated()
+select te