These are needed (among other things) for a TurboFan-generated
StringAddStub. Furthermore, they can be used to nuke the overly
complex %_IsInstanceType intrisic, it's completely expressible in
JavaScript now, but that will be done in a separate CL.

Alpha-sorted things a bit on the way to ease navigation.

Review URL: https://codereview.chromium.org/1010973010

Cr-Commit-Position: refs/heads/master@{#27415}