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/Lib/asyncio/streams.py b/Lib/asyncio/streams.py
index 204eaf7..e56e2ef 100644
--- a/Lib/asyncio/streams.py
+++ b/Lib/asyncio/streams.py
@@ -556,7 +556,7 @@
             # Avoid inheritance from FlowControlMixin
             # Copy-paste the code to your project
             # if you need flow control helpers
-            warnings.warn(f"{self.__class__} should be instaniated "
+            warnings.warn(f"{self.__class__} should be instantiated "
                           "by asyncio internals only, "
                           "please avoid its creation from user code",
                           DeprecationWarning)