cmComputeLinkInformation: prepare Item consumers for `OBJECT` libraries After b665966933 (cmComputeLinkInformation: track `OBJECT` library dependencies, 2023-07-22), introduced in !8645 as a fix for #25112, `OBJECT` libraries were tracked in a separate member to reduce the risk of further regressions. This commit prepares consumers to handle `OBJECT` libraries once they start appearing as link items.