Replace HtmlAgilityPack with AngleSharp

[OndrejVrsan]

Problem definition

While Kentico 11 CMS App has a dependency on AngleSharp, Kentico AMP uses HtmlAgilityPack, which provides a similar functionality. It's redundant to have both.

Suggested solution

Get rid of the HtmlAgilityPack dependency and replace it with AngleSharp.
Note: AngleSharp does not support XPaths, the code needs to be rewritten to LINQ for AngleSharp.

[rsuzumura]

Hi, I want to help on that refactoring, can you assign this issue to me? Thanks!

[petrsvihlik]

@rsuzumura absolutely, go ahead!