AthContainers: Add isAvailable methods taking a container.
Add to the Accessor classes versions of isAvailable that take a container as an argument, as well as an element.
In support of !73627 / ATLASRECTS-8008.
Add to the Accessor classes versions of isAvailable that take a container as an argument, as well as an element.
In support of !73627 / ATLASRECTS-8008.