`--rendering-backend=cocoa` is not supported despite being listed with `--list-rendering-backends`

[mwestphal]

Describe the bug
--rendering-backend=cocoa is not supported despite being listed with --list-rendering-backends, these option should be coherent.

Expected behavior
--rendering-backend=cocoa working and similar to --rendering-backend=auto

System Information:

• OS: macOS
• GPU and GPU driver: Any

F3D Information
Paste the content of f3d --version or f3d-console.exe --version on Windows:

Additional context
There is fonctionnaly no difference between auto and cocoa on macOS, its just for coherency.

[kaili-yang]

@mwestphal My PC is Mac Mini 4, and I'd like to take this.

[mwestphal]

@mwestphal My PC is Mac Mini 4, and I'd like to take this.

You already have two assigned issues though: https://github.com/f3d-app/f3d/issues?q=is%3Aissue%20state%3Aopen%20assignee%3Akaili-yang

[kaili-yang]

Make sense. I'm not gonna take this one and also please unassign me #3398 because I don't have time to wait for blocking issue.