Group/Annotation lookup performance

[bendikberg]

Purpose

This PR replaces the node hashset in annotations (groups) with a dictionary. The reason for this is to enable looking up group nodes by guid. Currently this is mostly done by searching for guids using linq queries, which means the node hashset serves no purpose.

Performance

All node-by-guid queries on groups will be sped up (unless the number of nodes in the group is very very small), this scales much better to large groups.

Declarations

Check these if you believe they are true

• [ ] The codebase is in a better state after this PR
• [ ] Is documented according to the standards
• [ ] The level of testing this PR includes is appropriate
• [ ] User facing strings, if any, are extracted into *.resx files
• [ ] All tests pass using the self-service CI.
• [ ] Snapshot of UI changes, if any.
• [ ] Changes to the API follow Semantic Versioning and are documented in the API Changes document.
• [ ] This PR modifies some build requirements and the readme is updated
• [ ] This PR contains no files larger than 50 MB

Release Notes

(FILL ME IN) Brief description of the fix / enhancement. Use N/A to indicate that the changes in this pull request do not apply to Release Notes. Mandatory section

Reviewers

@mjkkirschner

FYIs

@dimven