Don't convert URLs inside `<pre>` and `<code>` tags when parsing string using `make_clickable()`.
Adds Unit Tests.

Props johnjamesjacoby, helen, nacin, adamsilverstein, sirbrillig. 
Fixes #23756.



git-svn-id: https://develop.svn.wordpress.org/trunk@26052 602fd350-edb4-49c9-b593-d223f7449a82