Avoid relying on jQuery patches. Instead:
* use `CSS.escape` instead of `jQuery.escapeSelector`
* use `.filter()` with a proper handler instead of `.even()`
Keep `jquery-patch.js` for backwards compatibility, though.
Also, add tests for jquery-patch.
Ref gh-2249
jQuery positional selectors () have been deprecated in
[jQuery 3.4.0](https://blog.jquery.com/2019/04/10/jquery-3-4-0-released/)
and they'll be removed in jQuery 4.0.0. This PR removes their usage.
Most of the changes were possible without changing public API. However,
dropping `:even` usage required a change to the
[`header` option](https://api.jqueryui.com/accordion/#option-header)
of the accordion widget. I made it an optional function; this will need
to be documented.
The polyfill for `.even()` & `.odd()` is added for jQuery <3.5.0. There was
no usage of the :odd selector in the code but the `.odd()` method is also
polyfilled for completeness.
Closes gh-1904
