Fix and clean up skeletal animation (#15722)

* Fix attachments lagging behind their parents (#14818)
* Fix animation blending (#14817)
* Bring back cool guy as another .x smoke test
* Add .x mesh loader unittest
* Do bounding box & matrix calculation at proper point in time
* Remove obsolete `SAnimatedMesh`

irr/include/IMesh.h

@@ -20,38 +20,6 @@ enum E_ANIMATED_MESH_TYPE
 	//! Unknown animated mesh type.
 	EAMT_UNKNOWN = 0,
 
-	//! Quake 2 MD2 model file
-	EAMT_MD2,
-
-	//! Quake 3 MD3 model file
-	EAMT_MD3,
-
-	//! Maya .obj static model
-	EAMT_OBJ,
-
-	//! Quake 3 .bsp static Map
-	EAMT_BSP,
-
-	//! 3D Studio .3ds file
-	EAMT_3DS,
-
-	//! My3D Mesh, the file format by Zhuck Dimitry
-	EAMT_MY3D,
-
-	//! Pulsar LMTools .lmts file. This Irrlicht loader was written by Jonas Petersen
-	EAMT_LMTS,
-
-	//! Cartography Shop .csm file. This loader was created by Saurav Mohapatra.
-	EAMT_CSM,
-
-	//! .oct file for Paul Nette's FSRad or from Murphy McCauley's Blender .oct exporter.
-	/** The oct file format contains 3D geometry and lightmaps and
-	can be loaded directly by Irrlicht */
-	EAMT_OCT,
-
-	//! Halflife MDL model file
-	EAMT_MDL_HALFLIFE,
-
 	//! generic skinned mesh
 	EAMT_SKINNED,
 
@@ -119,9 +87,7 @@ public:
 	virtual void setDirty(E_BUFFER_TYPE buffer = EBT_VERTEX_AND_INDEX) = 0;
 
 	//! Returns the type of the meshes.
-	/** This is useful for making a safe downcast. For example,
-	if getMeshType() returns EAMT_MD2 it's safe to cast the
-	IMesh to IAnimatedMeshMD2.
+	/** This is useful for making a safe downcast.
 	Note: It's no longer just about animated meshes, that name has just historical reasons.
 	\returns Type of the mesh  */
 	virtual E_ANIMATED_MESH_TYPE getMeshType() const