All: Remove usage of jQuery positional selectors

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

1 files changed, 17 insertions, 0 deletions

diff --git a/ui/jquery-1-7.js b/ui/jquery-1-7.js
index 5e7907a15..3d0870f7c 100644
--- a/ui/jquery-1-7.js
+++ b/ui/jquery-1-7.js
@@ -98,4 +98,21 @@ if ( !$.uniqueSort ) {
 	$.uniqueSort = $.unique;
 }
 
+// Support: jQuery 3.4.x or older
+// These methods have been defined in jQuery 3.5.0.
+if ( !$.fn.even || !$.fn.odd ) {
+	$.fn.extend( {
+		even: function() {
+			return this.filter( function( i ) {
+				return i % 2 === 0;
+			} );
+		},
+		odd: function() {
+			return this.filter( function( i ) {
+				return i % 2 === 1;
+			} );
+		}
+	} );
+}
+
 } ) );