ref [ENG-661](https://linear.app/tryghost/issue/ENG-661/)
ref [ONC-253](https://linear.app/tryghost/issue/ONC-253/)
ref [PLG-174](https://linear.app/tryghost/issue/PLG-174/)
- restored the original but reverted fix for unsaved changes modal from https://github.com/TryGhost/Ghost/pull/20687
- updated code to remove some incorrect early-falsy-return logic in `editorController.hasDirtyAttributes` that prevented save of unsaved changes on the underlying model (e.g. excerpt)
- updated unit tests so they are testing real post model instances and therefore are testing what we expect them to test
- added acceptance tests to ensure autosave is working for title and excerpt fields
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Co-authored-by: Ronald Langeveld <hi@ronaldlangeveld.com>
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