Backport: Getting canonical sitemap item explicitly might result in random one if multiple canonical sitemap items match

@QA : for reproduction:

Start up testsuite, and then go to

http://localhost:8080/site/restapi/news/2008/11/partner-event.html

In there, the second link should be
<link href="/site/news/2008/11/partner-event.html

and not
<link href="/site/news2/2008/11/partner-event.html
or <link href="/site/news1/2008/11/partner-event.html

Problem:

In LocationMapResolver, there is #getCanonicalItem

That method returns if there are multiple equally well suited canonical sitemap items (equal depth) the first canonicals.get(0);.

Instead, it should just like the 'non explicit canonical link creation' use the LowestDepthFirstAndThenLexicalComparator