[psd] Improve handling of Adjustment Layers without raster data

The PSD import feature currently generates images bosed on layer raster data. Adjustment layers may or may not include raster data, depending on the software used to generate the PSD.

- Photoshop typically stores raster data for adjustment layers such as Fill or Gradient layers.
- Photopea, on the other hand, omits this data to reduce file size (see [Photopea issue #5558](https://github.com/photopea/photopea/issues/5558)).

At present, adjustment layers without raster data are ignored during import. This behavior might be unexpected for users, who should be informed of what occurred.

### Goal
When importing a PSD file, if any adjustment layers are ignored due to missing raster data, display a dialog warning the user and listing the ignored layers.

#### Bonus
It would be ideal to support the import of Fill and Gradient layers even if they lack raster data:
- **Fill Layers**: These should be relatively easy to support.
- **Gradient Layers**: This might be more challenging, as Photoshop's gradient formulas are not publicly documented.