stdlib: remove the dependency on the injected modules

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.

test/ModuleInterface/ModuleCache/Inputs/check-is-forwarding-module.py

@@ -1,8 +1,8 @@
 import sys
 
 for input_path in sys.argv[1:]:
-    with open(input_path, 'r') as yaml_file:
+    with open(input_path, 'rb') as yaml_file:
         # Forwarding files are YAML files that start with '---'
-        if yaml_file.read(3) != '---':
+        if yaml_file.read(3) != b'---':
             print("swiftmodule '%s' is not a forwarding module!" % input_path)
             sys.exit(1)