bpo-38266: Revert bpo-37878: Make PyThreadState_DeleteCurrent() Internal (GH-16558)

Revert the removal of PyThreadState_DeleteCurrent() with documentation.
diff --git a/Doc/c-api/init.rst b/Doc/c-api/init.rst
index 0b7a84d..5456ad4 100644
--- a/Doc/c-api/init.rst
+++ b/Doc/c-api/init.rst
@@ -1035,6 +1035,14 @@
    :c:func:`PyThreadState_Clear`.
 
 
+   .. c:function:: void PyThreadState_DeleteCurrent()
+
+    Destroy the current thread state and release the global interpreter lock.
+    Like :c:func:`PyThreadState_Delete`, the global interpreter lock need not
+    be held. The thread state must have been reset with a previous call
+    to :c:func:`PyThreadState_Clear`.
+
+
 .. c:function:: PY_INT64_T PyInterpreterState_GetID(PyInterpreterState *interp)
 
    Return the interpreter's unique ID.  If there was any error in doing