Mostly rote conversion of `proc()` to `move||` (and occasionally `Thunk::new`)
Delete tests that are either no longer relevant or which have
duplicate tests around object types.
Update guide/intro to take into account the removal of `proc`.

cc @steveklabnick
Update emacs and vi modes.
Add some tests for obsolete code, sugar used in appropriate ways.
Temporarily remove issue #14039; it is fixed and re-added by PR #19438