Since https://github.com/swiftlang/swift/pull/75608, the performance of `std::string` <=> `Swift.String` conversions improved significantly. To make sure the workload is significant enough for the benchmark results to be noise-free, this bumps the size of Swift strings that are being tested.
`Swift.String` can be initialized from any other type with an unlabeled initializer, which is either going to use the `CustomStringConvertible` conformance, or reflection. We would like clients to use the most suitable initializer, which is the one that takes `std.string` as a parameter. For instance, that allows us to attach a doc comment to the initializer.
This change makes the initializer unlabeled to make sure it is chosed by overload resolution when a client invokes `String(myCxxString)`.