swift234

rework our representations of subscripts to not curry the indexes 
separately from the get/set value.  There is no exposed way in the
source language to use this, and this causes shorter term annoyance.

I chose to flatten the value and indices so the value comes first.
In principle, this allows us to completely eliminate our ObjC importer
thunks.  I haven't removed them though, because they might be useful
for something else.


Swift SVN r14049