Distribute a prebuilt swift-syntax binary

### Description

I think that it'd be great to also distribute swift-syntax as a prebuilt framework with every release, at least for Apple platforms (like https://github.com/realm/SwiftLint does).

We have been successfully experimenting with https://github.com/sjavora/swift-syntax-xcframeworks because the added build time to our CI builds when compiling swift-syntax from the source code is unacceptable.