Moving json-rpc-engine from merged-packages into the packages

[kanthesha]

1. The big leap
   Move migration target from merged-packages/ to packages/.
   Run yarn install in the root directory.
   Check that all tests are passing in migration target by running yarn workspace @metamask/ test.
2. Update downstream repos
   Add tsconfig reference paths for migration target in downstream packages and root.
   Bump migration target version in downstream packages and root.
   Notes on why this version bump needs to happen as part of this PR (import module shadowing): eth-json-rpc-provider migration - Integration into packages/ eth-json-rpc-provider migration - Integration into packages/ #1738 (comment)
3. Linter fixes
   Apply yarn constraints fixes to migration target package.json file: yarn constraints --fix (run twice).
   Identify validator fixes for CHANGELOG using yarn workspace @metamask/ changelog:validate and apply the diffs.
4. Resolve or TODO downstream errors
   If introducing the migration target breaks any downstream repos:
   Resolve simple errors
   Mark and ignore complex/blocked errors using @ts-expect-error TODO: annotations.
   Create a separate issue for resolving the marked errors as soon as the migration is completed.
   Fix provider, middleware type errors in NetworkController and downstream packages Fix provider type errors in NetworkController and its downstream packages #1823
5. Finalize merge
   Check that all tests are passing in all subpackages of core and CI.
   Merge packages/ directory into core main branch.