SE-0241: Explicit Encoded Offsets for String Indices

[SDGGiesbrecht (Jeremy David Giesbrecht)]

String’s ABI and UTF-8

String’s ABI and UTF-8 We just landed String’s proposed final ABI on master. This ABI includes some significant changes, the primary one being that native Swift strings are stored as UTF-8 where they were previously stored either as ASCII or UTF-16 depending on their contents. NSStrings are still lazily bridged in to String without copying. This does not immediately surface in the API, but allows for some important performance wins and gives a more consistent basis for future APIs providing ef…