gh-100227: Move the Dict of Interned Strings to PyInterpreterState (gh-102339)

We can revisit the options for keeping it global later, if desired.  For now the approach seems quite complex, so we've gone with the simpler isolation solution in the meantime.

https://github.com/python/cpython/issues/100227

Include/internal/pycore_global_objects.h

@@ -23,13 +23,6 @@ extern "C" {
 // Only immutable objects should be considered runtime-global.
 // All others must be per-interpreter.
 
-#define _Py_CACHED_OBJECT(NAME) \
-    _PyRuntime.cached_objects.NAME
-
-struct _Py_cached_objects {
-    PyObject *interned_strings;
-};
-
 #define _Py_GLOBAL_OBJECT(NAME) \
     _PyRuntime.static_objects.NAME
 #define _Py_SINGLETON(NAME) \
@@ -65,6 +58,8 @@ struct _Py_static_objects {
     (interp)->cached_objects.NAME
 
 struct _Py_interp_cached_objects {
+    PyObject *interned_strings;
+
     /* AST */
     PyObject *str_replace_inf;
 

Include/internal/pycore_runtime.h

@@ -163,7 +163,6 @@ typedef struct pyruntimestate {
     } types;
 
     /* All the objects that are shared by the runtime's interpreters. */
-    struct _Py_cached_objects cached_objects;
     struct _Py_static_objects static_objects;
 
     /* The following fields are here to avoid allocation during init.

Include/internal/pycore_unicodeobject.h

@@ -59,6 +59,7 @@ struct _Py_unicode_state {
     struct _Py_unicode_ids ids;
 };
 
+extern void _PyUnicode_InternInPlace(PyInterpreterState *interp, PyObject **p);
 extern void _PyUnicode_ClearInterned(PyInterpreterState *interp);