v0.0.0-10242-g9d8ef0bc6

[ir] Simplify the implementation of IntervalSet::Intersect

We weren't taking enough advantage of the structure of the problem. First, we were making unnecessary copies of our inputs & using overly-complex computations. Second, since we were already requiring normalized inputs, we're actually guaranteed normalized output.

#cleanup

PiperOrigin-RevId: 944263340