bpo-35081: Add Include/internal/pycore_tupleobject.h (GH-10705)

Move _PyTuple_ITEMS() to a new header file:
Include/internal/pycore_tupleobject.h
diff --git a/PCbuild/pythoncore.vcxproj b/PCbuild/pythoncore.vcxproj
index 34cd379..8aa4c06 100644
--- a/PCbuild/pythoncore.vcxproj
+++ b/PCbuild/pythoncore.vcxproj
@@ -127,6 +127,7 @@
     <ClInclude Include="..\Include\internal\pycore_pylifecycle.h" />
     <ClInclude Include="..\Include\internal\pycore_pymem.h" />
     <ClInclude Include="..\Include\internal\pycore_pystate.h" />
+    <ClInclude Include="..\Include\internal\pycore_tupleobject.h" />
     <ClInclude Include="..\Include\internal\pycore_warnings.h" />
     <ClInclude Include="..\Include\intrcheck.h" />
     <ClInclude Include="..\Include\iterobject.h" />