Client: bump dependencies

Bumped everything except Prettier as that will do some code changes.

react-scripts had a peerDependency on TS v4 but still works with v5 so
  an override in package.json is necessary to use TS5 (see
  facebook/create-react-app#13080)

i18next had a major version bump, nothing relevant to this project
  though:
  https://www.i18next.com/misc/migration-guide#v22.x.x-to-v23.0.0

Relevant tsconfig options were also bumped to enable using modern JS
APIs and emit newer code.

Also, webpack no longer complains about using top-level await in i18n.ts
so switch to using that.