[ATOM-14344][ATOM-13908] Merging skinned and static mesh motion shaders using an optional vertex stream (#1491)

[ATOM-14344][ATOM-13908] Merging skinned and static mesh motion shaders using an optional vertext stream. This removes the log spam "Mesh does not have all the required input streams. Missing 'POSITIONT0'." and allows Material::GetShaderCollection() to be const only as it was intended. The MeshFeatureProcessor also no longer needs to decide which motion vector shader to use, and therefore no longer has m_skinnedMeshWithMotion in the descriptor to acquire a mesh.

Gems/AtomLyIntegration/EMotionFXAtom/Code/Source/AtomActorInstance.cpp

@@ -628,7 +628,10 @@ namespace AZ
             {
                 MeshHandleDescriptor meshDescriptor;
                 meshDescriptor.m_modelAsset = m_skinnedMeshInstance->m_model->GetModelAsset();
-                meshDescriptor.m_isSkinnedMeshWithMotion = true;
+
+                // [GFX TODO][ATOM-13067] Enable raytracing on skinned meshes
+                meshDescriptor.m_isRayTracingEnabled = false;
+
                 m_meshHandle = AZStd::make_shared<MeshFeatureProcessorInterface::MeshHandle>(
                     m_meshFeatureProcessor->AcquireMesh(meshDescriptor, materials));
             }