Bridge LocalizedStringKey as FormattableString

[chkn]

In both C# and F#, FormattableString can be created directly from an interpolated string literal, just like LocalizedStringKey in SwiftUI. We should be able to inspect the FormattableString and extract the format string and its arguments. Then we can use those to build up the LocalizedStringKey.StringInterpolation object and pass that to LocalizedStringKey.init(stringInterpolation:)