This adds testing for Store(Distinct(...)) with and without filters, to verify that
we can, in fact, store the results of a Distinct() query directly. This was at one
point unsupported, now we think it should work so we're testing it.
The change to the testdata is because the specific structure used for this test doesn't
work with a keyed index, and changing things to be "foreign keys" seems annoying and
more complicated, but possibly that should become part of a future test.
There was talk of testing this with non-BSI fields, but they don't seem to
actually work with Distinct right now, so that will be later.