Do mousemove timing in javascript, rather than in java.   This is getting intermittent failures on Tree_dnd.html but I think I can resolve them after the next checkin, where I monitor events on the document to tell when java robot actually executes each command.   Refs #15590 !strict.

git-svn-id: http://svn.dojotoolkit.org/src/dojo/trunk@29202 560b804f-0ae3-0310-86f3-f6aa0a117693
(cherry picked from commit 0eb6042a4a93aaf709d134f8ce1aadc1a13aa6f9)