Add [contains|matches][own]Whole

[jhy]

After reviewing #876 and the related #576. I think we can make some improvements, and also maintain backwards compatibility:

• (done) for :contains(text), normalize the selector text in the same way that the text() and ownText() methods work. That directly fixes this issue. I conceptually like the neatness of using :contains("text") to use a non-normalized search, but that's a bit stringly typed, and maybe backwards in-compat.
• (done) introduce :containsWholeText and :containsWholeOwnText which uses wholeText() and wholeOwnText() and no normalization to either the input or the query. That way we can find content including newlines, tabs, repeated spaces, etc
• (done) for Can't select elements with only whitespace #576, introduce :matchesWholeText and :matchesWholeOwnText, to work similarly for regular expressions

[xiaoxianma]

@jhy Hi Jon, I'm interested in this ticket. Is this done? Is there anything I can help with for this ticket?

[jhy]

Thanks @xiaoxianma for your offer; I've completed these, but you're of course welcome to hit up other issues / help with PRs etc.