Add a dedicated editor for Camera2D limits

[KoBeWi]

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This improves #101427 by replacing default rect edit with a dedicated editor (and also fixes multiple Camera2DEditor bugs). The main benefit is that camera is no longer selected when clicking within it's limit rectangle. In a separate commit I added functionality for overriding 2D editor's cursor, which makes the editor much more friendly.

https://github.com/user-attachments/assets/ba9deb13-e1c0-4948-8938-1aafbe9090c5

We could apply it to other existing editors, e.g. CollisionShape2D editor.

Closes #105077 Fixes #107409