(core) Let a confirmation default to canceling

Summary:
A confirmation dialog answers Enter with its action, which suits a question
whose answer can be taken back. Where it cannot, a dialog can now ask for the
opposite. Cancel takes the primary styling and answers Enter, and the action
turns red.

Two dialogs had done this by hand, each with half of it. Both now take their
buttons from the same place, which moves one of their Cancels to sit after the
action, as it does elsewhere.

Five more ask for it, each for something nothing can put back. Dialogs the undo
stack or the trash can reverse are left alone.

Test Plan: added tests

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D5057