Add a dialog for customizing FBX import

[reduz]

• If FBX files are found, a dialog will pop up asking to configure FBX2GLTF
• Dialog can also be accessed by going Editor -> Configure FBX Import
• The dialog also shows a link to click to download the converter, which should contain instructions.
• Noticed LinkButton does not allow specifying an url, so added this (supersedes Add a uri property to LinkButton #30675 )

Note that the link is non functional yet. The website needs to be created.

[fire-forge]

Noticed LinkButton does not allow specifying an url, so added this.

Does this supercede #30675 then?

[reduz]

@fire-forge yeah I guess

[fire]

Reviewed the overview design and it looks good. Did not go over in fine detail.

[akien-mga]

This class is only relevant of the FBX importer exists, so it should go in the modules/gltf/editor/ folder together with the importer.

[akien-mga]

The only thing I don't know yet how to do if moving this as I suggested, is how to the entry in the Settings menu.

[fire]

Need a rebase.

[reduz]

@fire feel free to take it over if you want

[fire]

@akien-mga I think I need to remake the branch or can I edit reduz's branch?

[YuriSizov]

@fire If you want, you can push to reduz's fork. We just need to be sure he doesn't delete it 🙃

[fire]

I completely forgot about this code.

[akien-mga]

I'm updating #30675 to get it merged, I'll rework this PR then.

[akien-mga]

It's not perfect but it should be good enough to merge, in parallel with godotengine/FBX2glTF#27 and godotengine/godot-website#392.

[akien-mga]

Let's merge this for now, can be improved further later on.

Changes done.

[akien-mga]

Thanks!