Live, reactive view over all contributions to a multi capability.
The collection is not a barrier: entries may be added or removed as plugins are
enabled/disabled — consume reactively.
Reactive atom of the current contributions, for Atom-based composition (e.g. a reactive
OperationHandlerSet). The manager memoizes one atom per capability, so this is the same
instance atom returns for the same capability.
Live, reactive view over all contributions to a multi capability. The collection is not a barrier: entries may be added or removed as plugins are enabled/disabled — consume reactively.