Test casts in remove_virtual_function()

Add a test to check that when we replace virtual function calls with
static function calls we cast the class to the appropriate type for the
static function call, so the argument for the `this` parameter will
have the correct type, and also that when a cast is not needed we will
not create one. Different code is run if there is only one possible
static function or if there is more than one, so we make sure that we
test both of these options.

Author: Owen Jones

regression/cbmc-java/remove_virtual_function_typecast/VirtualFunctions$A.class

@@ -0,0 +1,27 @@
+public class VirtualFunctions {
+  Object static_object;
+
+  public static class A {
+    public void f() {
+    }
+  }
+
+  public static class B extends A{
+    public void f() {
+    }
+  }
+
+  public static class C extends B {
+  }
+
+  public static void check(A a, B b, C c) {
+    // multiple possibilities, one needs a cast
+    a.f();
+
+    // single possibility, does not need a cast
+    b.f();
+
+    // single possibility, needs cast
+    c.f();
+  }
+}

regression/cbmc-java/remove_virtual_function_typecast/VirtualFunctions$B.class

@@ -0,0 +1,8 @@
+CORE
+VirtualFunctions.class
+--lazy-methods --java-max-vla-length 48 --unwind 8 --java-unwind-enum-static --trace --cover location --function VirtualFunctions.check --show-goto-functions
+ \(struct VirtualFunctions\$B \*\)a \. VirtualFunctions\$B\.f:\(\)V\(\);$
+ a \. VirtualFunctions\$A\.f:\(\)V\(\);$
+ b \. VirtualFunctions\$B\.f:\(\)V\(\);$
+ \(struct VirtualFunctions\$B \*\)c \. VirtualFunctions\$B\.f:\(\)V\(\);$
+--