This is needed to unblock nightly toolchains, which are currently failing to build with an assertion:
```
swift-frontend: /home/build-user/build/buildbot_linux/llvm-linux-x86_64/tools/clang/include/clang/AST/TypeNodes.inc:79: TypeInfo clang::ASTContext::getTypeInfoImpl(const Type *) const: Assertion `!T->isDependentType() && "should not see dependent types here"' failed.
```
rdar://150067288
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)`.
