Add rules to discourage #file and #filePath

[jqsilver]

Summary

Add lint rules to discourage the use of #file and #filePath literals (macros in 5.9).

In addition, my editor removed some trailing whitespace - let me know if I should revert that.

Reasoning

1. #file's behavior is changing in future Swift versions (https://developer.apple.com/documentation/swift/file), from the problematic behavior of #filePath to the more ideal behavior of #fileID. We should just use the literal/macro with explicit and unchanging behavior.
2. The documentation for #filePath says "Because #fileID doesn’t embed the full path to the source file, unlike #filePath, it gives you better privacy and reduces the size of the compiled binary. Avoid using #filePath outside of tests, build scripts, or other code that doesn’t become part of the shipping program." https://developer.apple.com/documentation/swift/filepath, so we should reflect this guidance in our lint rules.

Please react with 👍/👎 if you agree or disagree with this proposal.

[calda]

@jqsilver, could you also add a lint rule for this to https://github.com/airbnb/swift/blob/master/Sources/AirbnbSwiftFormatTool/swiftlint.yml?

[jqsilver]

@calda I added a lint rule for #file. Should I also add one for #filePath? It's harder to exempt tests and tools from a rule about #filePath

[calda]

We can follow how the no_direct_standard_out_logs rule is set up, and not exempt test targets in the swiftlint.yml file in this repo (even though we exempt test targets / demo modules etc in the swiftlint.yml file in the apps repo). Folks using our style tool can manually add // swiftlint:disable annotations as necessary (this is what we do in the Epoxy and Lottie repos).