AthContainers, etc: Add IConstAuxStore::getDecorIDs().
Add an interface to IConstAuxStore to get the set of decorations. This is to allow efficiently skipping decorations when we copy elements. See ATLASRECTS-8008.
Add an interface to IConstAuxStore to get the set of decorations. This is to allow efficiently skipping decorations when we copy elements. See ATLASRECTS-8008.