Make wxDumpWindow() public and available in wxMSW too

This function was defined in wxGTK and wxOSX, but not in wxMSW or the
other ports, but it can be useful there too, so make it public and
define it in common code.

tests/misc/guifuncs.cpp

@@ -201,3 +201,16 @@ TEST_CASE("GUI::FindWindowAtPoint", "[guifuncs]")
     INFO("Point over disabled child controls still corresponds to this child");
     CHECK( GetLabelOfWindowAtPoint(parent, 31, 111) == btn3->GetLabel() );
 }
+
+TEST_CASE("wxWindow::Dump", "[window]")
+{
+    CHECK_NOTHROW( wxDumpWindow(NULL) );
+
+    wxScopedPtr<wxButton>
+        button(new wxButton(wxTheApp->GetTopWindow(), wxID_ANY, "bloordyblop"));
+
+    const std::string s = wxDumpWindow(button.get()).utf8_string();
+
+    CHECK_THAT( s, Catch::Contains("wxButton") );
+    CHECK_THAT( s, Catch::Contains("bloordyblop") );
+}