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/Python/ast.c b/Python/ast.c
index ce3b492..976be70 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -5256,7 +5256,7 @@
     *str += 1;
 
     /* If we're in = mode (detected by non-NULL expr_text), and have no format
-       spec and no explict conversion, set the conversion to 'r'. */
+       spec and no explicit conversion, set the conversion to 'r'. */
     if (*expr_text && format_spec == NULL && conversion == -1) {
         conversion = 'r';
     }