swift

de780834 - [rbi] Change IsolationHistory::MergeElementRegions to store the rhs value of the merge separately from the rest of the elements in its region.

[rbi] Change IsolationHistory::MergeElementRegions to store the rhs value of the merge separately from the rest of the elements in its region. We previously did not truly represent that we stored the rhs element of the merge that allowed us to find the old region in a real way into the node. Now it is part of the node's API so we can always know the actual operands to the merge.