Fix same importer will be added multiple times in get_importers_for_extension

[jsjtxietian]

Fixes #92710

The problem lies in the fact that both EditorSceneFormatImporterUFBX and EditorSceneFormatImporterFBX2GLTF can import .fbx, so local_exts for scene importer will contain duplicate fbx entry.

I suppose we can also make local_exts a unique set instead of list? But put a break here seems reasonable.

[AThousandShips]

LGTM

[akien-mga]

What does this imply for actually being able to choose which importer to use? Like choosing between ufbx and fbx2gltf in the import settings.

[AThousandShips]

This makes it so that each importer is added just once, it doesn't stop multiple importers from being selected, it just doesn't add the same importer for each matched extension

Though it might be better to identify why it has multiple different identical extensions

[jsjtxietian]

What does this imply for actually being able to choose which importer to use?

IMHO what the import dock (or shall we say the current importer abstraction ) supports now is to choose a importer, it's up to the importer itself (like in this case, a scene importer) to decide how to import this file.

[akien-mga]

Thanks!