Draft: Eraser toggle and paint mode toggle
This MR creates an action to toggle the current tool to the Eraser. A shortcut can then be applied to this action so that the user can toggle to the eraser whilst painting, and back again to whatever tool they were painting in. It also creates an action to toggle the current paint mode to erase,so that the user can toggle to erase mode whilst painting, and back again to whatever mode they were painting in.
This is could be an answer to this -> https://gui.gimp.org/index.php?title=Usability_and_Tools
For digital drawing, I want the eraser to be a minimum size, not a sharp pencil, so I toggle the eraser tool. For painting, I want to erase with the current brush, so I toggle paint mode. This is being tested as a workflow. Perhaps the paint mode switching is not necessary, more testing is needed. The code works, it could be improved with a better test than string comparison, and the way I've hacked in context changes into the menu system looks bad. I'll try and highlight these issues in the comments.