Inject the necessary module maps and apinotes via the VFS. This cleans
up the developer build in preparation for a secondary change to remove
this need for deployed scenarios as well. Injecting the content via the
VFS will enable us restore the ability to work with a pristine
installation of Visual Studio, dropping the custom action for the Swift
installer, and open the pathway to per-user installation of Swift.
Thanks to @bnbarham for the help and discussion in resolving the test
issues.
The `__future__` we relied on is now, where the 3 specific things are
all included [since Python 3.0](https://docs.python.org/3/library/__future__.html):
* absolute_import
* print_function
* unicode_literals
* division
These import statements are no-ops and are no longer necessary.
Prebuilt-module directory now contains a SystemVersion.plist file copied from the SDK
it's built from. This patch teaches the compiler to remark this version and the SDK version
when -Rmodule-interface-rebuild is specified. The difference between these versions could
help us debug unusable prebuilt modules.
