Post-migration cleanup for `@metamask/json-rpc-middleware-stream`

[MajorLift]

Tasks

• Update README to reflect new status as a non-root package in core monorepo.
• Add migration target to README dependency graph using the generate-dependency-graph build script.
  • Update root README dependency graph with @metamask/json-rpc-{engine,middleware-stream} #1991
• Fix downstream errors that were marked with @ts-expect-error TODO: during the migration process.
• Record any changes made to packages during the migration process in their respective CHANGELOGs.
  • Record CHANGELOG entries from @metamask/json-rpc-{engine,middleware-stream} migrations #2003
• Use the yarn create-release-branch tool to publish a release of core with a new version for the migrated package and any updated downstream packages.
• Publish typedocs with GitHub Pages.

References

• See #1551 (comment) for context on the migration process.
• See #1079 (comment) for context on the migration initiative.

[desi]

@MajorLift Can you add an estimate to this one?