[Fuchsia] Import test scripts from chromium and use it to download image

The with_envs.py works with the test script by providing the required
environment variables.

This change in theory does nothing since the `product download` is in
12.20230413.0.1, but `run` is removed before that,
https://fxrev.dev/831319. So the DEPS cannot really download the images.
The issue will be addressed in a coming change.

Bug: #38752
Change-Id: Ib5f3d1d619921651208fa442201ba607a99e54d5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/319867
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Alexander Thomas <athom@google.com>
Commit-Queue: Zijie He <zijiehe@google.com>

.gn

@@ -15,3 +15,12 @@ secondary_source = "//build/secondary/"
 
 # Override the default script executable to always be python3.
 script_executable = "python3"
+
+default_args = {
+  # fuchsia::io::InotifyWatchMask has been deprecated in 12 and removed in 13
+  # right before the current version (12.20230418.0.1) we are using.
+  # https://fxrev.dev/836377.
+  # So explicitly marking fuchsia_target_api_level to 11 to workaround it
+  # temporarily.
+  fuchsia_target_api_level = 11
+}