Should rename `IHtmlContentBuilder.Append(IHtmlContent)` to `IHtmlContentBuilder.AppendHtml(IHtmlContent)`

[NTaylorMullen]

This is a pre-requisite to this issue and has the same reasoning. Essentially it's already decently confusing when determining how to append encoded/unencoded content. This would help make it clearer since IHtmlContent is HTML.

[hishamco]

IMHO Append is make since while it's a member of IHtmlContentBuilder unless we can append non-html content

[dougbu]

The language here is never going to be quite right. An IHtmlContent implementation may or may not be pre-encoded. And, while IHtmlContent is intended to write out HTML content, that should be obvious from the instance type; why repeat that inference in this particular method name?