fuchsia: Include reference to zx library

"library zx" used to be built in to fidlc, but is now a standalone file
(this is an SDK change). Update the build rules to adapt to this.

ref: https://logs.chromium.org/logs/crashpad/buildbucket/cr-buildbucket.appspot.com/8883567878548782112/+/steps/compile_with_ninja/0/stdout

FAILED: gen/fidl/include/fuchsia/sysinfo/c/client.cc gen/fidl/include/fuchsia/sysinfo/c/fidl.h gen/third_party/fuchsia/fidl/fuchsia.sysinfo/tables.c gen/third_party/fuchsia/fidl/fuchsia.sysinfo/intermediary_representation.json
python ../../third_party/fuchsia/runner.py ../../third_party/fuchsia/sdk/linux-amd64/tools/fidlc --c-header gen/fidl/include/fuchsia/sysinfo/c/fidl.h --c-client gen/fidl/include/fuchsia/sysinfo/c/client.cc --tables gen/third_party/fuchsia/fidl/fuchsia.sysinfo/tables.c --json gen/third_party/fuchsia/fidl/fuchsia.sysinfo/intermediary_representation.json --name fuchsia.sysinfo --files ../../third_party/fuchsia/sdk/linux-amd64/fidl/fuchsia.sysinfo/sysinfo.fidl
../../third_party/fuchsia/sdk/linux-amd64/fidl/fuchsia.sysinfo/sysinfo.fidl:7:7: error: Could not find library named zx. Did you include its sources with --files?
using zx;
      ^~

Bug: fuchsia:7802
Change-Id: I10c0109fd9621a19d72deb21a489c2041caeeeca
Reviewed-on: https://chromium-review.googlesource.com/c/crashpad/crashpad/+/2141019
Commit-Queue: Scott Graham <scottmg@chromium.org>
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Justin Cohen <justincohen@chromium.org>

third_party/fuchsia/BUILD.gn

@@ -156,6 +156,8 @@ if (crashpad_is_in_fuchsia) {
         "--name",
         fidl_source.library_name,
         "--files",
+        rebase_path("$sdk_fidl_sources_path/zx/zx_common.fidl", root_build_dir),
+        "--files",
         rebase_path(fidl_source.fidl, root_build_dir),
       ]