Feature: Improve support for flattening folders

### What feature or improvement do you think would benefit Files?

Would love an option to dissolve or flatten a folder. Placing all the content in the parent folder.
Simply said, it's the opposite of "Create folder with selection" and placing it above or below this entry would make the most sense.
Example:

- 📁 Parent folder
- 📄 File A
- 📁 Sub-folder _(target this folder)_
- 📄 File B
- 🖼 File C

Would give:

- 📁 Parent folder
- 📄 File A
- 📄 File B
- 🖼 File C

### Requirements

- [x] Add action to command palette for flattening folders when a single folder is selected
- [ ] Conflict prompt should show for conflicting/duplicate files
- [ ] Display progress in status center
- [ ] Enable option when multiple folders are selected

### Files Version

2.4.71

### Windows Version

Windows 10

### Comments

I've seen many, many requests for this in the PowerToys repo, so I **know** it's something people want.
- https://github.com/microsoft/PowerToys/issues/9269