Fuchsia: Implement vectors-of-more-things in FIDL/JS

Vectors of primitive types and strings were previously implemented; this
extends support to vectors of unions and structs.

Bug: 883496
Change-Id: Id00174b05d04c3f432fae39112afde658e533806
Reviewed-on: https://chromium-review.googlesource.com/c/1318676
Commit-Queue: Scott Graham <scottmg@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605826}
3 files changed