This version removes nalexander's lovely matrix code. It turned out
that scalar and tuple bindings are sufficiently different from coll
and rel -- they can directly apply as values in the query -- that
there was no point in jumping through hoops to turn those single
values into a matrix.
Furthermore, I've standardized us on a Vec<TypedValue>
representation for rectangular matrices, which should be much
more efficient, but would have required rewriting that code.
Finally, coll and rel are sufficiently different from each other
-- coll doesn't require processing nested collections -- that
my attempts to share code between them fell somewhat flat. I had
lots of nice ideas about zipping together cycles and such, but
ultimately I ended up with relatively straightforward, if a bit
repetitive, code.
The next commit will demonstrate the value of this work -- tests
that exercised scalar and tuple grounding now collapse down to
the simplest possible SQL.
* Part 1: define ValueTypeSet.
We're going to use this instead of `HashSet<ValueType>` so that we can clearly express
the empty set and the set of all types, and also to encapsulate a switch to `EnumSet`."
* Part 2: use ValueTypeSet.
* Part 3: fix type expansion.
* Part 4: add a test for type extraction from nested `or`.
* Review comments.
* Review comments: simplify ValueTypeSet.
