This introduces a compiler pass that schedules the graph and re-wires effect chain according to the schedule. It also connects allocating representation changes to the effect chain, and removes the BeginRegion and EndRegion nodes - they should not be needed anymore because all effectful nodes should be already wired-in.
This is an intermediate CL - the next step is to move lowering of the Change*ToTaggedEffect nodes to StateEffectIntroduction so that we do not have to introduce the effectful versions of nodes.
Review URL: https://codereview.chromium.org/1849603002
Cr-Commit-Position: refs/heads/master@{#35565}
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