[Mosaic:TPU] Add relayout for adding minor implicit dim and relax some offset restrictions on similar shape cast

[copybara-service[bot]]

[Mosaic:TPU] Add relayout for adding minor implicit dim and relax some offset restrictions on similar shape cast

This factors out some logic from the apply-vector-layout shape cast rule where we insert a minor dimension, relaxes some offset restrictions on it, and uses it for the relayout.