[UX] When uninstalling a module, list all things that will be lost (blocks, views, menus) in the confirmation page.

This came up in https://github.com/backdrop/backdrop-issues/issues/570#issuecomment-1848... and is related to #678.

We need a way for modules to communicate to the user what they are used for in their website before they are completely uninstalled. A good place would be the uninstallation confirmation page/dialog.