Webpack bundles compile but need further testing. Jest + mocha tests
compile but are marked as `manual` until further work is done to get them
passing. The four jest tests are green and enabled now, though.
## Test plan
`bazel build //client/...` and `bazel test //client/...`
Bazel's rules_js rely on the pnpm package manager. To simplify the integration, we're migrating to pnpm from our current package manager — yarn. Another reason to migrate is that pnpm is cool and fast. 😉
