Add a feature to container_internal::Layout that lets you specify some array sizes at compile-time as template parameters. This can make offset and size calculations faster.

In particular, it seems to always improve the performance of AllocSize(), and it sometimes improves the performance of other functions, e.g. when the Layout object outlives the function that created it.

PiperOrigin-RevId: 616817169
Change-Id: Id1d318d7d2af68783f9f59090d89c642be6ae558