tools: improve valgrind support

- Generate and use a list of suppressions that reduce noisiness for
  known (non-)issues.
- Use `--zero-fill-buffers` for tests, as they sometimes use
  `Buffer.allocUnsafe()` and valgrind reports that as usage
  of uninitialized memory.

PR-URL: https://github.com/nodejs/node/pull/25498


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>