[IROutliner] Fix phi nodes when self referential within block but doesn't contain branch

When outlining a phi node, if the the incoming branch is a block contained in the region and the branch from that block is not outlined, we create broken code. The fix is to recognize when that branch from the included incoming block is not contained, and ignore the region.

Reviewer: paquette

Differential Revision: https://reviews.llvm.org/D121311