Include vendored dependencies to the default ignore filename regex list

[Altair-Bueno]

Introducction

Crates that from private organizations often use vendored sources (e.g chain of trust requirements, CI/CDs without network access...). It would be great if cargo-llvm could pick these vendored sources and exclude them automatically.

Current behaviour

Vendored sources count towards the coverage report

Expected behaviour

Vendored sources should not count towards the coverage report

Possible solutions

• Pick up source.*.directory from .cargo/config.toml and exclude them automatically
• Always exclude the vendor folder: It won't cover all cases, but is a great default

[taiki-e]

This seems reasonable to me. I would accept a PR to do this.