dgram: make UDPWrap more reusable

Allow using the handle more directly for I/O in other parts of
the codebase.

Originally landed in the QUIC repo

Original review metadata:

```
  PR-URL: https://github.com/nodejs/quic/pull/165


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
```

Signed-off-by: James M Snell <jasnell@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/31871


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>