Returns true iff the Asset is a TopLevelAsset (not a subobject, its outer is aUPackage). Only TopLevelAssets can be PrimaryAssets in the AssetManager. A TopLevelAsset is not necessarily the main asset in a package; see IsUAsset. Note that this is distinct fromUObject::IsAssetbecause IsAsset can be overloaded (see e.g.AActor::IsAsset)