Summary:
UBSAN was running, but failures were not being treated as such by bazel. This fixes that.

After enforcing UBSAN, had to make a few fixes, including an upgrade to rapidjson.

Test Plan: Existing tests.

Reviewers: zasgar, #engineering

Reviewed By: zasgar, #engineering

Differential Revision: https://phab.corp.pixielabs.ai/D5656

GitOrigin-RevId: 67cf1b58933ff6d65bb75774c155ce317250da59