Do not highlight inside of hrefs

[OndrejSpanel]

Naive highlighting results in URLs like:

https://threejs.org/examples/#webgl_shadowmap_%3Cspan%20class='search-highlight'%3Ecsm%3C/span%3E

No highlighting should be done inside of <> of HTML tags.

Again result of searching for CSM in three.js, this time in https://www.github.com/mrdoob/three.js/issues/11840