A way to exit ui editor mode in prefab editor

[xxSeys1]

Issue description:

When you add a ui canvas to a prefab that also has 3D objects in it it's impossible to exit the ui editor to the 3D editor.

Put a button that appears when the ui edit mode is enables that allows the user to go back to the 3D editor at the marked location;

As an icon maybe use a 3D cube.

Steps to reproduce:

1. Create an ui canvas in a prefab that has 3D stuff in it

Minimal reproduction project:

none

Flax version:

1.8.1