This adds a new API built with the `ValueBoundsConstraintSet` to compute
the bounds of possibly scalable quantities. It uses knowledge of the
range of vscale (which is defined by the target architecture), to solve
for the bound as either a constant or an expression in terms of vscale.

The result is an `AffineMap` that will always take at most one
parameter, vscale, and returns a single result, which is the bound of
`value`.

The API is defined as follows:

```c++
FailureOr<ConstantOrScalableBound>
vector::ScalableValueBoundsConstraintSet::computeScalableBound(
  Value value, std::optional<int64_t> dim,
  unsigned vscaleMin, unsigned vscaleMax,
  presburger::BoundType boundType, 
  bool closedUB = true,
  StopConditionFn stopCondition = nullptr);
```

Note: `ConstantOrScalableBound` is a thin wrapper over the `AffineMap`
with a utility for converting the bound to a single quantity (i.e. a
size and scalable flag).

We believe this API could prove useful downstream in IREE (which uses a
similar analysis to hoist allocas, which currently fails for scalable
vectors).