Swt::Transform dispose

This PR covers disposal of the `Swt::Transform` resources that we allocate in Shoes. From my search, this includes `Shoes::Swt::Common::Painter`, `Shoes::Swt::Line` and `Shoes::Swt::Shape`.

`Shoes::Swt::Common::Painter` seems the most frequent one in a basic app with text for me, but this should get them all covered.

Part of #649.