Add revealAll feature to Import PSD

Photoshop2Spine script has a `revealAll` features that allows to activate/deactivate layers cropping at the canvas. It can be enabled [by code](https://github.com/EsotericSoftware/spine-scripts/blob/master/photoshop/PhotoshopToSpine.jsx#L19), not using the UI.

Currently this feature has a bug: it never crops at the canvas, as if it always `revealAll` set to `true`.

The goal of this task is to implement the feature in the Spine Import PSD, adding a new checkbox `[ ] Reveal all` at the right of `[ ] Ignore hidden layers`.

As a further step, we could fix the `revealAll` not working in the script.

- [ ] Add `revealAll` feature to Import PSD with a new checkbox
- [ ] Fix the `revealAll` in Photoshop2Spine

Related forum threads:
- https://esotericsoftware.com/forum/d/27213-psd%E6%AA%94%E5%8C%AF%E5%87%BA%E7%9A%84%E8%A3%81%E5%88%87%E5%95%8F%E9%A1%8C
- https://esotericsoftware.com/forum/d/27222-issue-with-cropping-in-photoshoptospine-script%E5%85%B3%E4%BA%8Ephotoshoptospine%E8%84%9A%E6%9C%AC%E7%9A%84%E8%A3%81%E5%88%87%E9%97%AE%E9%A2%98/5
- https://esotericsoftware.com/forum/d/15015-suggestion-ps-export-script-canvas-clipping-issue