Avoid raw mode parsing so that raw mode tags like <script> don't cause issues.

Certain tags like <script> but also <title> and others switch an HTML5 parser
into raw mode, which causes the rest of the HTML string to be always parsed as
text, including any elements or entities that we do want to support (e.g. <p>).

As we're going to escape any of the raw text elements anyway (it's e.g. script,
style, title, xmp, noframes, and a couple of others) we can just switch of raw
text parsing by disabling it after each starting tag.