[ConstantRangeTest] Make exhaustive testing more principled (NFC)

[ConstantRangeTest] Make exhaustive testing more principled (NFC)

The current infrastructure for exhaustive ConstantRange testing is
somewhat confusing in what exactly it tests and currently cannot even
be used for operations that produce smallest-size results, rather than
signed/unsigned envelopes.

This patch makes the testing more principled by collecting the exact
set of results of an operation into a bit set and then comparing it
against the range approximation by:

 * Checking conservative correctness: All elements in the set must be
   in the range.
 * Checking optimality under a given preference function: None of the
   (slack-free) ranges that can be constructed from the set are
   preferred over the computed range.

Implemented preference functions are:

 * PreferSmallest: Smallest range regardless of signed/unsigned wrapping
   behavior. Probably what we would call "optimal" without further
   qualification.
 * PreferSmallestUnsigned/Signed: Smallest range that has no
   unsigned/signed wrapping. We use this if our calculation is precise
   only up to signed/unsigned envelope.
 * PreferSmallestNonFullUnsigned/Signed: Smallest range that has no
   unsigned/signed wrapping -- but preferring a smaller wrapping range
   over a (non-wrapping) full range. We use this if we have a fully
   precise calculation but apply a sign preference to the result
   (union/intersection). Even with a sign preference, returning a
   wrapping range is still "strictly better" than returning a full one.

This also addresses PR49273 by replacing the fragile manual range
construction logic in testBinarySetOperationExhaustive() with generic
code that isn't specialized to the particular form of ranges that set
operations can produces.

Differential Revision: https://reviews.llvm.org/D88356