Fix typos in comments, docs and test names (#15018)

* Fix typos in comments, docs and test names

* Update test_pyparse.py

account for change in string length

* Apply suggestion: splitable -> splittable

Co-Authored-By: Terry Jan Reedy <tjreedy@udel.edu>

* Apply suggestion: splitable -> splittable

Co-Authored-By: Terry Jan Reedy <tjreedy@udel.edu>

* Apply suggestion: Dealloccte -> Deallocate

Co-Authored-By: Terry Jan Reedy <tjreedy@udel.edu>

* Update posixmodule checksum.

* Reverse idlelib changes.
diff --git a/Include/abstract.h b/Include/abstract.h
index f36fafb..8951f63 100644
--- a/Include/abstract.h
+++ b/Include/abstract.h
@@ -702,7 +702,7 @@
      (PyList_Check(o) ? PyList_GET_ITEM(o, i) : PyTuple_GET_ITEM(o, i))
 
 /* Return a pointer to the underlying item array for
-   an object retured by PySequence_Fast */
+   an object returned by PySequence_Fast */
 #define PySequence_Fast_ITEMS(sf) \
     (PyList_Check(sf) ? ((PyListObject *)(sf))->ob_item \
                       : ((PyTupleObject *)(sf))->ob_item)