Resolve "Nodejs 17 breaks webpack 5"

This MR fixes nodejs 17+ compatibility:

• Use the xxhash64 algorithm, as md4 is no longer available.
• Use the webpack5 entrypoint for react-pdf, since the legacy entrypoint used md4 hashing.
  • Adds a polyfill for buffer, as it is not provided by nodejs 17.
• Changes the proxy url to 127.0.0.1, as localhost can default to [::1] (ipv6) in nodejs 17+

Closes #667 (closed)