Viewport.js: Added user camera preview function.

[1993heqiang]

Description
Some functions of the user's camera preview are realized, including position movement, rotation, and zooming.

PS:
When I added a custom camera in the editor, and then switched to the custom camera, I found that the objects in the scene could not be operated, so I modified it. This modification is based on my personal thoughts. If you have any comments, please let me know.

[Mugen87]

I'm afraid this changes goes in the wrong direction. The idea is to implement a switch for changing between orthographic and perspective cameras like outlined here: #16008.

It's not intended that the cameras from the selection box replace the default editor camera. It's also not appropriate to introduce OrbitControls to the editor.

[1993heqiang]

I'm afraid this changes goes in the wrong direction. The idea is to implement a switch for changing between orthographic and perspective cameras like outlined here: #16008.

It's not intended that the cameras from the selection box replace the default editor camera. It's also not appropriate to introduce OrbitControls to the editor.

I did not see this discussion #16008 before submitting the PR. I also agree with your views. :)