Re-add "instant" scroll behavior as default for scroll into view. (#1924)

This reverts commit 957235e.

Author: whimboo

index.html

@@ -4496,6 +4496,9 @@ <h2>Elements</h2>
   the following <a><code>ScrollIntoViewOptions</code></a>:
 
   <dl>
+   <dt>"<code>behavior</code>"
+   <dd>"<code>instant</code>"
+
    <dt><a>Logical scroll position "<code>block</code>"</a>
    <dd>"<code>end</code>"