Rework multiple spec and multiple targets for delayed modifier

[jsonn]

Description

If multiple nodes are targetted by one trigger specification, they share a delay. This is useful e.g. for active searches with multiple participating fields, so that the search triggers only when search modifiers have been processed.

If a node has multiple triggers with the delay modifier, they act independently. This corresponds to the logic from #2026.

Corresponding issue: #2892

This PR is the successor for #2893.

Testing

New tests have been added as appropriate.

Checklist

• [X] I have read the contribution guidelines
• [X] I have targeted this PR against the correct branch (master for website changes, dev for source changes)
• [ ] This is either a bugfix, a documentation update, or a new feature that has been explicitly approved via an issue
• [X] I ran the test suite locally (npm run test) and verified that it succeeded