bpo-36842: Implement PEP 578 (GH-12613)

Adds sys.audit, sys.addaudithook, io.open_code, and associated C APIs.
diff --git a/PCbuild/pythoncore.vcxproj b/PCbuild/pythoncore.vcxproj
index df57adc..681c4db 100644
--- a/PCbuild/pythoncore.vcxproj
+++ b/PCbuild/pythoncore.vcxproj
@@ -129,12 +129,14 @@
     <ClInclude Include="..\Include\cpython\abstract.h" />
     <ClInclude Include="..\Include\cpython\coreconfig.h" />
     <ClInclude Include="..\Include\cpython\dictobject.h" />
+    <ClInclude Include="..\Include\cpython\fileobject.h" />
     <ClInclude Include="..\Include\cpython\object.h" />
     <ClInclude Include="..\Include\cpython\objimpl.h" />
     <ClInclude Include="..\Include\cpython\pyerrors.h" />
     <ClInclude Include="..\Include\cpython\pylifecycle.h" />
     <ClInclude Include="..\Include\cpython\pymem.h" />
     <ClInclude Include="..\Include\cpython\pystate.h" />
+    <ClInclude Include="..\Include\cpython\sysmodule.h" />
     <ClInclude Include="..\Include\cpython\traceback.h" />
     <ClInclude Include="..\Include\cpython\tupleobject.h" />
     <ClInclude Include="..\Include\cpython\unicodeobject.h" />