[GlobalISel] Combine mulo x, 2 -> addo x, x

Similar to what SDAG does when it sees a smulo/umulo against 2
(see: `DAGCombiner::visitMULO`)

This pattern is fairly common in Swift code AFAICT.

Here's an example extracted from a Swift testcase:

https://godbolt.org/z/6cT8Mesx7

Differential Revision: https://reviews.llvm.org/D110662