This is part of the development component for the module and is part of
the interface definition. This content is consumed by the user during
development.
Extract the `install_swift_interface` function into a new file. This
is always invoked to perform the installation of the Swift interfaces as
well as the binary module. Additionally, it prepares for a future
refactoring which will also install the swift documentation interface.
Add the next stage of the runtimes build - the overlays. This homes the
platform specific overlays for the libraries and is required to make
further progress towards a static SDK for Windows.
