[ticket/17326] Add font icon field for custom BBCodes

Adds a new field to the custom BBCode add/edit form that
allows admins to define a Font Awesome icon to be displayed
instead of the BBCodes name on the posting.php editor page.

PHPBB-17326

phpBB/adm/style/admin.js

@@ -277,5 +277,10 @@ function parse_document(container)
 		$('.actions a:has(i.acp-icon)').mouseover(function () {
 			$(this).css("text-decoration", "none");
 		});
+
+		// Live update BBCode font icon preview
+		$('#bbcode_font_icon').on('keyup', function(e) {
+			$('#bbcode_icon_preview').attr('class', "o-icon o-icon-font fa-fw fas icon fa-" + $(this).val());
+		});
 	});
 })(jQuery);