refs https://github.com/TryGhost/Team/issues/609
There's a 3 second timeout before a background save is triggered after the last edit, if the preview modal is opened in that timeframe it would show outdated content.
- added a task that is triggered when the preview modal is opened
- if a save task is already running it will wait for it to finish
- otherwise if the post is a draft and the editor has dirty attributes it will trigger a save
- modal shows a loading spinner whilst waiting for the save to finish so the preview contents always match the latest editor changes
refs https://github.com/TryGhost/Team/issues/559
- moved the modal component class, template, and sub-components into a `components/modals/` directory to keep the top-level dir cleaner
- migrated component class to full glimmer syntax
