Refine node mesh scaling logic

We now do scale static meshes, as the bug that caused meshes not to be scaled was limited to skeletally animated meshes,
hence we ought not to reproduce it for skinned meshes that do not take advantage of skeletal animations (e.g. current MTG doors).

However, gltf models (e.g. Wuzzy's eyeballs) up until recently were always affected due to technical reasons
(using skeletal animation for rigid animation).

Thus, to preserve behavior, we:

1. Do not apply 10x scale to glTF models.
2. Apply 10x scale to obj models.
3. Apply 10x scale to static x or b3d models, but not to animated ones.

irr/include/SkinnedMesh.h

@@ -339,6 +339,10 @@ public:
 		return AllJoints;
 	}
 
+	//! Whether the mesh originated from a glTF file.
+	//! This is important for legacy reasons.
+	bool isGltf() const { return IsGltf; }
+
 protected:
 	void checkForAnimation();
 
@@ -382,12 +386,14 @@ protected:
 	bool PreparedForSkinning;
 	bool AnimateNormals;
 	bool HardwareSkinning;
+
+	bool IsGltf = false;
 };
 
 // Interface for mesh loaders
 class SkinnedMeshBuilder : public SkinnedMesh {
 public:
-	SkinnedMeshBuilder() : SkinnedMesh() {}
+	SkinnedMeshBuilder(bool is_gltf = false) : SkinnedMesh() { IsGltf = is_gltf; }
 
 	//! loaders should call this after populating the mesh
 	// returns *this, so do not try to drop the mesh builder instance

irr/src/CGLTFMeshFileLoader.cpp

@@ -347,7 +347,7 @@ IAnimatedMesh* SelfType::createMesh(io::IReadFile* file)
 	const char *filename = file->getFileName().c_str();
 	try {
 		tiniergltf::GlTF model = parseGLTF(file);
-		irr_ptr<SkinnedMeshBuilder> mesh(new SkinnedMeshBuilder());
+		irr_ptr<SkinnedMeshBuilder> mesh(new SkinnedMeshBuilder(true));
 		MeshExtractor extractor(std::move(model), mesh.get());
 		try {
 			extractor.load();