Reland "[dawn][native] Remove error injector symbols when not enabled"

This reverts commit dae002bc90363c7ca04bc6bcc6cad4e76c724277.

Reason for revert: Fixed fuzzer build. The easiest way to reproduce this
is with these GN args:
  use_libfuzzer = true
  dawn_enable_error_injection = false
I'm not sure exactly why the settings in the Chrome build (see link
below) built the fuzzers without dawn_enable_error_injection, though.

Also incorporates Ryan's CMake fix. Note this enables building
VulkanErrorInjectorTests with CMake (the rule for which referenced the
undefined variable) which previously was never possible.

Original change's description:
> Revert "[dawn][native] Remove error injector symbols when not enabled"
>
> This reverts commit 58b146a9831a06e04c0d3d7a1194f227c56b9f08.
>
> Reason for revert: breaks Dawn wire server fuzzer on roll into Chromium
>
> Failure Link: https://ci.chromium.org/ui/p/chromium/builders/try/linux-rel/2894192/overview
>
> Original change's description:
> > [dawn][native] Remove error injector symbols when not enabled
> >
> > EnableErrorInjector() and friends were confusingly allowed even when
> > DAWN_ENABLE_ERROR_INJECTION was not enabled. Fix that by simply not
> > defining them in that case.
> >
> > Bug: 553115993
> > Change-Id: If725259e5cff89122ae4cf7e9682a4158830722e
> > Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/341095
> > Auto-Submit: Kai Ninomiya <kainino@chromium.org>
> > Reviewed-by: Brandon Jones <bajones@chromium.org>
> > Commit-Queue: Brandon Jones <bajones@chromium.org>
>
> # Not skipping CQ checks because original CL landed > 1 day ago.
>
> Bug: 553115993
> Change-Id: I189e943cdb17f653770137a6866b863ed1952fe0
> Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/341695
> Reviewed-by: dan sinclair <dsinclair@chromium.org>
> Commit-Queue: dan sinclair <dsinclair@chromium.org>
> Reviewed-by: Ryan Harrison <rharrison@chromium.org>
> Commit-Queue: James Price <jrprice@google.com>
> Auto-Submit: James Price <jrprice@google.com>

Bug: 553115993
Change-Id: Id26f39adfa655e8f5a34e35535a7b3a1a6e3a2b0
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/342335
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Kai Ninomiya <kainino@chromium.org>