v8: upgrade 3.21.18.3
src: update after v8 api changes
build: fix test-gc weakref build rule

Make the build rule depend on the build artifact (weakref.node) itself
rather than the directory it's built in.  Depending on the directory
means that a build failure won't trigger a rebuild on the next
invocation because the directory's timestamp has been updated.
test: fix up weakref.cc after v8 api change
http client: pull last chunk on socket close

When the socket closes, the client's http incoming message object was
emitting an 'aborted' event if it had not yet been ended.

However, it's possible, when a response is being repeatedly paused and
resumed (eg, if piped to a slow FS write stream), that there will be a
final chunk remaining in the js-land buffer when the socket is torn
down.

When that happens, the socketCloseListener function detects that we have
not yet reached the end of the response message data, and treats this as
an abrupt abort, immediately (and forcibly) ending the incoming message
data stream, and discarding that final chunk of data.

The result is that, for example, npm will have problems because tarballs
are missing a few bytes off the end, every time.

Closes GH-6402