Replace cheerio with DOMParser

The node-html-parser emulates the behavior of the browser's DOMParser, which is the standard API for parsing HTML. It has also proven itself to be much faster. The node-html-parser package is also 5M smaller (2.2M vs 7.2M). Furthermore, Antora will be integrating node-html-parser to provide a built-in API for extensions to use to parse HTML (see antora#1120). All of these reasons point to replacing cheerio with the node-html-parser package in this project.