Backport: Do not touch module with #![rustfmt::skip] (#4297)

[ytmimi]

Summary

When working to fix issue #5033 in PR #5035 I proposed a solution to extended the span of the root module to include all content within the file (including trailing comments).

The PR was accepted because rustfmt should have a view of the entire file, but @calebcartwright and I agreed that the preferred solution would be to ignore files completely if they contain the #![rustfmt::skip] attribute.

#4297 introduces code that correctly skips files marked with the #![rustfmt::skip] attribute, but we need to review the changes before we can backport them into 1.x