dojo/on: fix event handling broken on Safari iOS 8 beta. Refs #18168

Rework dojo/on's way to decide about using event delegation. Now uses feature detection, which fixes the event handling currently broken on Safari iOS 8 beta (including beta 4).

Remarks:
* The newly introduced has-feature is added only if has("touch") is truthy for consistency with the fact the feature is only intended for touch-enabled devices (hence the "touch-" prefix in its name), and it is only used in dojo/on inside a `if(has("touch")){ ... }`.
* Tested on Safari iOS 6/7/8b, various Android (Chrome, stock, FF), IE/WP8, BB Z10.