[mw.loader] Refactor addInlineCSS's logic, fixing various bugs

[mw.loader] Refactor addInlineCSS's logic, fixing various bugs

* Using mw.util.addCSS as base to instance of bug 33305 automatically
* Expose as mw.loader.addStyleTag
* Re-use the code in mw.util.addCSS
* Drop the "text > Cdata > element > jQuery object > innerHTML", in favor of setting cssText or appending a text node (html escapement isn't a problem when working with text nodes directly).
* Appending this way also works in IE, no need for the dispose/re-create style-tag logic in the try-catch().

* Follows-up r110988 (fixme)