[META][D8][UX] Convert all confirmation pages to confirmation dialogs instead.

I had filed a couple of separate issues for this back in 2015, about specific pages. Let's make this issue here a meta to list all such issues.

First step would be:

• [ ] #3771 | [UX] Introduce a confirm_dialog() function (and use that one instead of confirm_form())

Specific confirmation pages to be converted to dialogs:

• [ ] #769 | [UX] Move the confirmation dialog for deletion of nodes to a modal.
• [ ] #770 | [UX] Move the confirmation dialog for deletion of menu links to a modal.
• [ ] #3770 | [UX] Move the confirmation dialog for enabling/uninstalling modules to a modal.

Related D8 issues:

• Add abstracted dialog to core (resolves accessibility bug)
• [META] Convert all confirm forms already converted to new routing system to use modal dialog

(Triaged as possible accessibility issue on 08/17/2921. This one may or many not qualify, please add the [A11Y] tag if you think it qualifies.)