Spec relies on implicit task queuing, mixing up setFocusBehavior() timing

[jan-ivar]

This spec settles promises in parallel, relying on implicit behavior removed in whatwg/webidl#490 (comment):

• Fix all call sites of "resolve a promise" etc. to explicitly queue a task, instead of the current implicit task queuing. This fixes Promise-manipulation shorthands have underdefined behavior w3ctag/promises-guide#52.

This causes confusion over what order tasks are queued in the setFocusBehavior steps. We should make it explicit to avoid confusion.