While the primary use-case for Suspend nodes is the Yield expression,
there are other uses as well: Await expressions, and the initial suspend
of Generators, which returns an object matching the Iterator protocol.

"Suspend" is a better representation of the spec text (closer
to the spec text for the values of [[GeneratorState]] and
[[AsyncGeneratorState]]), and can make it easier to understand the
meaning of what I had previously called Yield::is_normal() (now
Suspend::is_yield()).

Changes requested as part of https://chromium-review.googlesource.com/c/447117/

BUG=
R=neis@chromium.org, adamk@chromium.org
TBR=bmeurer@chromium.org, paul.lind@imgtec.com, joransiu@ca.ibm.com, weiliang.lin@intel.com

Change-Id: Ic6f15b04fff091c20f26526391b967287c06f6bf
Reviewed-on: https://chromium-review.googlesource.com/455583Reviewed-by: Caitlin Potter <caitp@igalia.com>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44038}