bpo-46008: Make runtime-global object/type lifecycle functions and state consistent. (gh-29998)

This change is strictly renames and moving code around.  It helps in the following ways:

* ensures type-related init functions focus strictly on one of the three aspects (state, objects, types)
* passes in PyInterpreterState * to all those functions, simplifying work on moving types/objects/state to the interpreter
* consistent naming conventions help make what's going on more clear
* keeping API related to a type in the corresponding header file makes it more obvious where to look for it

https://bugs.python.org/issue46008

Include/internal/pycore_sliceobject.h

@@ -0,0 +1,20 @@
+#ifndef Py_INTERNAL_SLICEOBJECT_H
+#define Py_INTERNAL_SLICEOBJECT_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+#  error "this header requires Py_BUILD_CORE define"
+#endif
+
+
+/* runtime lifecycle */
+
+extern void _PySlice_Fini(PyInterpreterState *);
+
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTERNAL_SLICEOBJECT_H */