Rollup merge of rust-lang#79379 - GuillaumeGomez:no-js-not-hidden, r=Nemo157

Show hidden elements by default when JS is disabled

Fixes  rust-lang#79301.

A lot of things are hidden by default which shouldn't when JS is disabled. This PR fixes it.

Before:

![Screenshot from 2020-11-24 14-10-16](https://user-images.githubusercontent.com/3050060/100099361-a16d5580-2e5f-11eb-891b-a4c005aeb1d0.png)

After:

![after](https://user-images.githubusercontent.com/3050060/100099382-a6caa000-2e5f-11eb-8190-14f330aff9a2.png)

r? `@jyn514`

Author: GuillaumeGomez

src/librustdoc/html/static/noscript.css

@@ -1,3 +1,9 @@
+/*
+This whole CSS file is used only in case rustdoc is rendered with javascript disabled. Since a lot
+of content is hidden by default (depending on the settings too), we have to overwrite some of the
+rules.
+*/
+
 #main > h2 + div, #main > h2 + h3, #main > h3 + div {
 	display: block;
 }
@@ -13,3 +19,7 @@
 #main > h2 + h3 {
 	display: flex;
 }
+
+#main .impl-items .hidden {
+	display: block !important;
+}