Change default parenting behavior when drag-and-dropping to 2d and 3d editor

[Nodragem]

Implement this proposal: godotengine/godot-proposals#9682

Note: I was thinking to add a label and label_desc in the 3D editor as it is in the 2D editor. But I think it might need its own proposal.

• Bugsquad edit, closes: Make "add as sibling" the default when drag-and-dropping an asset into 3D View godot-proposals#9682

[ryevdokimov]

Tested 2D and 3D, looks good. Just needs to fix code style/formatting.

Hoping this makes it in for 4.3, I find the current behavior to be very unintuitive and the justifications in the proposal seem sound.

[AdriaandeJongh]

Yes please to this PR! An excellent UX improvement.

[Nodragem]

The formatting should be ok now? Let me know if there are any issues.

Edit: In terms of making it for 4.3, I hope this PR can be considered a bug fix, as the current behaviour is accidental from the interaction between 2 different PRs (as explained in the proposal).

[akien-mga]

For the record, your commit seems not to be linked to your GitHub account. See: Why are my commits linked to the wrong user? for more info.

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Also while fixing style issues, please make sure to squash the commits into one.

[Nodragem]

I think I fixed eveything you've mentionned 🚀 !

[KoBeWi]

The code looks ok.

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉