bpo-36543: Revert "bpo-36543: Remove the xml.etree.cElementTree module." (GH-20117) (GH-20780)

* Revert "bpo-36543: Remove the xml.etree.cElementTree module. (GH-19108)"

This reverts commit b33e52511a59c6da7132c226b7f7489b092a33eb.
(cherry picked from commit ec88e1bca81a167e6d5c0ac635e22f84298cb1df)
diff --git a/Lib/xml/etree/cElementTree.py b/Lib/xml/etree/cElementTree.py
new file mode 100644
index 0000000..368e679
--- /dev/null
+++ b/Lib/xml/etree/cElementTree.py
@@ -0,0 +1,3 @@
+# Deprecated alias for xml.etree.ElementTree
+
+from xml.etree.ElementTree import *