expose mesh cache and GetMeshId

Runtime/Scripts/GLTFSceneExporter.cs

@@ -1146,6 +1146,20 @@ public TextureId GetTextureId(GLTFRoot root, UniqueTexture textureObj)
 			}
 			return null;
 		}
+
+		public MeshId GetMeshId(Mesh meshObj)
+		{
+			foreach (var primOwner in _primOwner)
+			{
+				// Not sure if this is entirely accurate – we're returning the first instance here.
+				if (primOwner.Key.Mesh == meshObj)
+				{
+					return primOwner.Value;
+				}
+			}
+
+			return null;
+		}
 
 		public ImageId GetImageId(GLTFRoot root, Texture imageObj, TextureExportSettings textureMapType)
 		{

Runtime/Scripts/GLTFSceneImporter.cs

@@ -223,6 +223,7 @@ public GameObject LastLoadedScene
 		public MaterialCacheData[] MaterialCache => _assetCache.MaterialCache;
 		public AnimationCacheData[] AnimationCache => _assetCache.AnimationCache;
 		public GameObject[] NodeCache => _assetCache.NodeCache;
+		public MeshCacheData[] MeshCache => _assetCache.MeshCache;
 
 		/// <summary>
 		/// Whether to keep a CPU-side copy of the mesh after upload to GPU (for example, in case normals/tangents need recalculation)