[Extensions] Fix entry points for Screen Orientation Extension

After commit 856353beba8a8318c51da3d672af187d7fd58ada, entitled
"[Extensions] Add a setter callback accessor to trampolines",
we can now use screen.onorientationchange as a valid entry point.
Merge pull request #1481 from jeez/fix-screen-orientation

[Extensions] Fix entry points for Screen Orientation Extension