Do not report missing third party files

[La0]

https://sentry.prod.mozaws.net/operations/code-coverage-bot/issues/6370196/

Path third_party/rust/unicode-xid/src/tables.rs not found in report

[La0]

We should parse the third party exclusion list and avoid reporting those files as missing when uploading to Phabricator

[La0]

And also check that the extension is supported, i see lots of warning around rust & webidl files...