This commit is a follow up to a recent overhaul of the GetPage/ref/relref implemenation.
The most important change in this commit is the update to `.Site.GetPage`:
* To reduce the amount of breakage in the wild to its minimum, I have reworked .Site.GetPage with some rules:
* We cannot support more than 2 arguments, i.e. .Site.GetPage "page" "posts" "mypage.md" will now throw an error. I think this is the most uncommon syntax and should be OK. It is an easy fix to change the above to .Site.GetPage "/posts/mypage.md" or similar.
* .Site.GetPage "home", .Site.GetPage "home" "" and .Site.GetPage "home" "/" will give you the home page. This means that if you have page in root with the name home.md you need to do .Site.GetPage "/home.md" or similar
This commit also fixes some multilingual issues, most notable it is now possible to do cross-language ref/relref lookups by prepending the language code to the path, e.g. `/jp/posts/mypage.md`.
This commit also reverts the site building tests related to this to "Hugo 0.44 state", to get better control of the changes made.
Closes#4147Closes#4727Closes#4728Closes#4728Closes#4726Closes#4652
