Update actor render bounding box (#991)

* Extend MeshFeatureProcessor to allow changing the mesh bbox, which requires re-compute the culling data for that mesh

* Update actor mesh bbox when EMFX actor instance bbox changes.

Also use the actor instance global bbox to compute the local bbox for the skinned render mesh, instead of the using the static bounds based bbox, as not every actor instance is going to be using the static bounds bbox.

* Store per-instance mesh AABB in the right place.

In the MeshInstanceData, which is unique per instance, instead of in the Model, which is shared between all instances.

For greater clarity, also remove Model::m_aabb and the corresponding getter and setter, as it isn't immediately obvious whether this gets the model asset bbox or the mesh instance bbox. Callers should instead be explicit about which bbox they want.

* Bug fix: model asset is not necessarily ready in AcquireMesh

* Remove now-unused forward declaration

* Update MockMeshFeatureProcessor with SetLocalAabb/GetLocalAabb

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

@@ -83,12 +83,20 @@ namespace AZ
         void AtomActorInstance::UpdateBounds()
         {
             // Update RenderActorInstance world bounding box
-            // The bounding box is moving with the actor instance. It is static in the way that it does not change shape.
+            // The bounding box is moving with the actor instance.
             // The entity and actor transforms are kept in sync already.
             m_worldAABB = AZ::Aabb::CreateFromMinMax(m_actorInstance->GetAABB().GetMin(), m_actorInstance->GetAABB().GetMax());
 
             // Update RenderActorInstance local bounding box
-            m_localAABB = AZ::Aabb::CreateFromMinMax(m_actorInstance->GetStaticBasedAABB().GetMin(), m_actorInstance->GetStaticBasedAABB().GetMax());
+            // NB: computing the local bbox from the world bbox makes the local bbox artifically larger than it should be
+            // instead EMFX should support getting the local bbox from the actor instance directly
+            m_localAABB = m_worldAABB.GetTransformedAabb(m_transformInterface->GetWorldTM().GetInverse());
+
+            // Update bbox on mesh instance if it exists
+            if (m_meshFeatureProcessor && m_meshHandle && m_meshHandle->IsValid() && m_skinnedMeshInstance)
+            {
+                m_meshFeatureProcessor->SetLocalAabb(*m_meshHandle, m_localAABB);
+            }
 
             AZ::Interface<AzFramework::IEntityBoundsUnion>::Get()->RefreshEntityLocalBoundsUnion(m_entityId);
         }