This makes some changes to the formatter so that ImportRefUnused and
ImportRefUsed will both be labeled as "import_ref" with an "unused ->
used" argument change in textual IR, but is otherwise not changing
logic.
I'd excluded these initially just because I was thinking towards copies,
but under the current model I'm trying to catch all the decl types just
for consistency. Note references will still be a TODO error
(LazyImportRef is already tested for this, it just didn't feel necessary
to add individual tests while I try to sort out behavior).
Fixes an oversight where declarations in an entity's scope were being
added to the list of exports.
Note I'm trimming some Import API arguments as now-unused.
Jon Ross-Perkins