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.
Working towards fixing issues in !73627 / ATLASRECTS-8008.
Add to the Accessor classes versions of isAvailable that take a container as an argument, as well as an element.
Working towards fixing issues in !73627 / ATLASRECTS-8008.