This is the next step towards faster Map and Set iteration. It
introduces the appropriate instance types for Map and Set
iterators (following the pattern for Array iterators) and migrates
the following builtins to the CodeStubAssembler:

  - Set.prototype.entries
  - Set.prototype.values
  - Map.prototype.entries
  - Map.prototype.keys
  - Map.prototype.values
  - %SetIteratorPrototype%.next
  - %MapIteratorPrototype%.next

This already provides a significant performance boost for regular
for-of iteration of Sets and Maps, by a factor of 5-10 depending
on the input. The final step will be to inline some fast-paths
into TurboFan.

Drive-by-fix: Remove obsolete %IsJSSetIterator and %IsJSMapIterator
intrinsics and runtime functions.

Bug: v8:6571, chromium:740122
Change-Id: Iad7a7dec643d8f8b5799327f89a351108ae856bf
Reviewed-on: https://chromium-review.googlesource.com/563399
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46492}