Deduplicate Yarn Dependencies

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Feature description

See https://github.com/dependabot/dependabot-core/issues/1297#issuecomment-1246727627 and below for the original discussion of this topic. As proposed in https://github.com/dependabot/dependabot-core/issues/1297#issuecomment-1264519762, one possible compromise would be to dedupe if and only if there are no preexisting duplicates (meaning `yarn dedupe` runs clean prior to bumping).

Start by reading the linked discussion in dependabot-core issue 1297, especially the referenced comments, to understand the proposed deduplication rule. Identify where Yarn dependency updates are assembled, then verify that deduplication runs only when no preexisting duplicates exist and that the resulting update behavior matches the proposal.

Written by the indexing model from the issue text.