Add Ghost Element for Drag & Drop move

[lookacat]

Description

See owncloud/web#5788

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Technical debt
• Tests

Checklist:

• Code changes
• Unit tests added
• Acceptance tests added
• Documentation added/updated

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[kulmann]

Some small things. But in general: wow! Awesome solution and improvement! 🥳 Looking forward to getting this merged.

[lookacat]

@pascalwengerter @kulmann In case you a wondering why i set the ghost elements position to be outside of the viewport instead of removing it after, if I remove the element after setting the drag image the drag image gets also removed, if i set the display none it does the same. Sadly I couldn't find a less hacky way.

[kulmann]

One thing to think about regarding a11y, otherwise LGTM 👍 Also checked it with a local link. Worked well for me.

[sonarqubecloud]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

12.5% Coverage
0.0% Duplication