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.

TBR=jgruber@chromium.org

Bug: v8:6344, v8:6571, chromium:740122
Change-Id: I3ab0ee49e2afe8d4295707a5ecbd51adda621918
Reviewed-on: https://chromium-review.googlesource.com/563626
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46497}