Remove unnecessary Array copy.
Remove unnecessary Array copy.

Array.append(contentsOf:) supports any Sequence, and String.UTF8View is
a sequence, so there's no need to create an Array from it to append it.

From a post-merge feedback in #2393.

apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation,apple/swift-corelibs-foundation