[swift-evolution] Use lowerCamelCase for @warn_unqualified_access attribute?

[Ben Rimmington]

I noticed that the @warn_unqualified_access attribute in LibraryEvolution hasn't been updated to lowerCamelCase.

<http://jrose-apple.github.io/swift-library-evolution/#methods>

It's currently used by the `min` and `max` methods of Sequence, and the `print` methods in AppKit.

<https://github.com/apple/swift/blob/0661f61/stdlib/public/core/SequenceAlgorithms.swift.gyb#L150-L166>

<https://github.com/apple/swift/blob/84cd5cc/lib/ClangImporter/ImportDecl.cpp#L6463-L6476>

It doesn't have the UserInaccessible option, so can @warn_unqualified_access also be used in client code?

<https://github.com/apple/swift/blob/173658a/include/swift/AST/Attr.def#L246-L247>

-- Ben