doc: add auto intrinsic height to prevent jitter/flicker

This commit addresses a scrolling/flickering issue in the HTML version
of the docs. By adding `auto` to the `contain-intrinsic-size` CSS
property, we're asking the browser to remember the last-rendered size
for the element (once it's been rendered) instead of forcing the browser
to treat it as being 1px by 5000px when it goes offscreen.

PR-URL: #48195
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>

doc/api_assets/style.css

@@ -436,7 +436,7 @@ dd + dt.pre {
 
 #apicontent section {
   content-visibility: auto;
-  contain-intrinsic-size: 1px 5000px;
+  contain-intrinsic-size: 1px auto 5000px;
 }
 
 #apicontent .line {