Use is_lint_allowed() for computationally heavy lints

[BD103]

By default, all lints are run, even if they are #[allow(...)]d. #[allow(...)] attributes are usually just taken in account when filtering out these diagnostics. This unfortunately can lead to slow lints being run, even if they're never used.

is_lint_allowed() solves this by letting lint passes check if a specific lint is allowed before it runs the heavy computation. While not applicable in all situations, it is useful for speeding up the linter by only running what we need.