[IROutliner] Adding outlining for single entry/single exit multiblock regions
Using the similarity found from the IRSimilarity Identifier, we take regions with structural similarity, and deduplicate them into a separate function. The Code Extractor is able to provide most of this functionality.
For simplicity, we start by only outlining regions with a single entry and single exit branch, this reduces the complexity in handling phi nodes outside the region, and handling many sets of outputs for each of the different exit blocks.
Differential Revision: https://reviews.llvm.org/D106990