Update widgets.css to use native disclosure widget marker, but enlarged

I have just read an article by Scott O'Hara (https://www.scottohara.me/blog/2022/09/12/details-summary.html), where he says that removing the native marker for the disclosure widget can cause accessibility problems because some assistive technology looks to the marker instead of the status of the `open` attribute to know whether the widget is open or not! Yes, it's completely crazy!

So this commit goes back to using the native marker but makes it bigger. Which, really, I suppose is what I should have done in the first place. I will submit a PR to make a similar change for the dashboard widgets, post metaboxes, and menu items that we've already included.

src/wp-admin/css/widgets.css

@@ -42,25 +42,16 @@ summary.widget-title {
 	user-select: none;
 }
 
-summary.widget-title {
-	list-style: none;
+.widget-title h3 {
+	padding-left: 5px;
 }
 
-summary.widget-title::before {
-	content: '\25B8';
+summary.widget-title::marker,
+summary.widget-title::-webkit-details-marker {
 	font-size: 1.4em;
 	cursor: pointer;
 }
 
-details[open] > summary.widget-title::before {
-	content: '\25BE';
-}
-
-/* Fix for Safari */
-summary.widget-title::-webkit-details-marker {
-	display: none;
-}
-
 .widgets-holder-wrap .widget-inside {
 	border: 0;
 	border-top: 1px solid #c3c4c7;
@@ -379,29 +370,14 @@ summary.sidebar-name {
 	color: #1d2327;
 	font-size: 1.3em;
 	font-weight: 600;
-	list-style: none;
 }
 
-summary.sidebar-name::before {
-	content: '\25B8';
-	padding-right: 0.5em;
+summary.sidebar-name::marker,
+summary.sidebar-name::-webkit-details-marker {
 	font-size: 1.2em;
 	cursor: pointer;
 }
 
-#widgets-right .widgets-holder-wrap > details > summary.sidebar-name::before {
-	padding-right: 0.2em;
-}
-
-details[open] > summary.sidebar-name::before {
-	content: '\25BE';
-}
-
-/* Fix for Safari */
-summary.sidebar-name::-webkit-details-marker {
-	display: none;
-}
-
 .widgets-holder-wrap .description {
 	padding: 0 0 15px;
 	margin: 0;