This commit pulls in the HTML Tag Processor from the Gutenbeg repository.
The Tag Processor attempts to be an HTML5-spec-compliant parser that provides the ability in PHP to find specific HTML tags and then add, remove, or update attributes on that tag. It provides a safe and reliable way to modify the attribute on HTML tags.
More information: https://github.com/WordPress/wordpress-develop/pull/3920.
Props: antonvlasenko, bernhard-reiter, costdev, dmsnell, felixarntz, gziolo, hellofromtonya, zieladam, flixos90, ntsekouras, peterwilsoncc, swissspidy, andrewserong, onemaggie, get_dave, aristath, scruffian, justlevine, andraganescu, noisysocks, dlh, soean, cbirdsong, revgeorge, azaozz.
Fixes#57575.
git-svn-id: https://develop.svn.wordpress.org/trunk@55203 602fd350-edb4-49c9-b593-d223f7449a82
