[VectorCombine] Scalarize binop-like intrinsics (#138095)

Currently VectorCombine can scalarize vector compares and binary ops.
This extends it to also scalarize binary-op like intrinsics like umax,
minnum etc.

The motivation behind this is to scalarize more intrinsics in
VectorCombine rather than in DAGCombine, so we can sink splats across
basic blocks: see #137786

This currently has very little effect on generated code because
InstCombine doesn't yet canonicalize binary intrinsics where one operand
is a constant into the form that VectorCombine expects, i.e. `binop
(shuffle insert) const --> shuffle (binop insert const)`. The plan is to
land this first and then in a subsequent patch teach InstCombine to do
the canonicalization to avoid regressions in the meantime.

This uses `isTriviallyVectorizable` to determine whether or not an
intrinsic is safe to scalarize. There's also `isTriviallyScalarizable`,
but this seems more geared towards the Scalarizer pass and includes
intrinsics with multiple return values.

It also only handles intrinsics with two operands with the same type as
the return type. In the future we would generalize this to handle
arbitrary numbers of operands, including unary operators too, e.g. fneg
or fma, as well as different operand types, e.g. powi or scmp

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