Primary motivation is documentation, but it will also hopefully simplify the code.
Also,
* Lower case the default output format names; this is in line with the custom ones (map keys) and how
it's treated all the places. This avoids doing `stringds.EqualFold` everywhere.
Closes#10896Closes#10620
And make both .Resources and resources implement it.
This gets us 2 new methods/functions, so you can now also do:
* .Resources.Get
* resources.ByType
Note that GetRemote is not covered by this interface, as that is only available as a global template function.
Fixes#8653
