[INTERNAL] sap.ui.core.element: delegate the implementation of .focus to
jQuery

- delegate the implementation of
the sap.ui.core.Element.prototype.focus() method to jQuery.sap.focus()
(code reuse)

Change-Id: Ic9f765f6add34c2e8c8024bd411e3cf873a7f21c
Merge "[INTERNAL] sap.ui.core.element: delegate the implementation of .focus to jQuery"