AthContainers+AthContainersInterfaces: Fix return value of AuxTypeVector::resize for null container

AuxTypeVector::resize is supposed to return false if iterators were invalidated. We were doing this by testing if the allocated block moves during the resize.

This was being used to know when caches must be invalidated.

However, if we resize an empty container that has reserved memory, then the the allocated block may not move. But in that case we were sometimes failing to invalidate a dependent cache.

Change so that we explicitly return false when increasing the size (and clarify documentation).