Fixes issue where multiple GS primitives ended up sharing the same scratch matrix as their draw command model matrix

The draw command doesn't take ownership of the underlying matrix, so whichever tileset went last won causing tilesets to shift incorrectly

draw command owner was also incorrectly set as "this" instead of primitive.

Author: keyboardspecialist

packages/engine/Source/Scene/GaussianSplatPrimitive.js

@@ -766,7 +766,7 @@ GaussianSplatPrimitive.buildGSplatDrawCommand = function (
   const modelMatrix = Matrix4.multiply(
     tileset.modelMatrix,
     Matrix4.fromArray(tileset.root.transform),
-    scratchMatrix4B,
+    new Matrix4(),
   );
 
   const vertexArrayCache = primitive._vertexArray;
@@ -780,7 +780,7 @@ GaussianSplatPrimitive.buildGSplatDrawCommand = function (
     cull: renderStateOptions.cull.enabled,
     pass: Pass.GAUSSIAN_SPLATS,
     count: renderResources.count,
-    owner: this,
+    owner: primitive,
     instanceCount: renderResources.instanceCount,
     primitiveType: PrimitiveType.TRIANGLE_STRIP,
     debugShowBoundingVolume: tileset.debugShowBoundingVolume,