Rollup merge of #98773 - notriddle:notriddle/source-sidebar-details, r=GuillaumeGomez

rustdoc: use <details> tag for the source code sidebar

This fixes the extremely poor accessibility of the old system, making it possible to navigate the sidebar by keyboard, and also implicitly gives the sidebar items the correct ARIA roles.

Split out separately from #98772

src/librustdoc/html/static/css/rustdoc.css

@@ -1578,37 +1578,22 @@ kbd {
 	margin-bottom: 1em;
 }
 
-div.children {
-	padding-left: 27px;
-	display: none;
-}
-div.name {
-	cursor: pointer;
-	position: relative;
-	margin-left: 16px;
-}
-div.files > a {
-	display: block;
-	padding: 0 3px;
-}
-div.files > a:hover, div.name:hover {
-	background-color: #a14b4b;
-}
-div.name.expand + .children {
-	display: block;
-}
-div.name::before {
-	content: "\25B6";
+details.dir-entry {
 	padding-left: 4px;
-	font-size: 0.625rem;
-	position: absolute;
-	left: -16px;
-	top: 4px;
 }
-div.name.expand::before {
-	transform: rotate(90deg);
-	left: -15px;
-	top: 2px;
+
+details.dir-entry > summary {
+	margin: 0 0 0 13px;
+	list-style-position: outside;
+	cursor: pointer;
+}
+
+details.dir-entry div.folders, details.dir-entry div.files {
+	padding-left: 23px;
+}
+
+details.dir-entry a {
+	display: block;
 }
 
 /* The hideme class is used on summary tags that contain a span with