backport of minor physics sample fixes for 1.2

Author: BrianWill-Unity

PhysicsSamples/Assets/9. Modify/Prefabs/ExplosionSpawner.prefab

@@ -30,7 +30,6 @@ Transform:
  m_ConstrainProportionsScale: 0
  m_Children: []
  m_Father: {fileID: 0}
- m_RootOrder: 0
  m_LocalEulerAnglesHint: {x: 0, y: 0, z: 0}
 --- !u!114 &7414927642867552315
 MonoBehaviour:
@@ -46,5 +45,5 @@ MonoBehaviour:
  m_EditorClassIdentifier: 
  Prefab: {fileID: 9019979733640190286, guid: b58133b914c853f43aaf1cd8cb3333a7, type: 3}
  Count: 200
- Countdown: 100
+ Countdown: 50
  Force: 500

PhysicsSamples/Assets/9. Modify/Scripts/Systems/RotateThroughCollisionFiltersSystem.cs

@@ -91,9 +91,8 @@ in SystemAPI.Query<RefRO<PhysicsCollider>, RenderMeshArray, RefRO<ChangeCollisio
 
  if (index > -1)
  {
- var newMeshInfo = MaterialMeshInfo.FromRenderMeshArrayIndices(
- index, 0);
- EntityManager.SetComponentData(entity, newMeshInfo);
+ var newMeshInfo = EntityManager.GetComponentData<MaterialMeshInfo>(entity);
+ newMeshInfo.Material = MaterialMeshInfo.ArrayIndexToStaticIndex(index);
  }
  }
  }