Enable testing flutter-embedder-test2

[richkadel]

When this test was originally added to the flutter/engine repo, the CI
test would not work because the Fuchsia test environment (based on
fuchsia's "terminal" product type) did not appear to include the
hardware-display-controller-provider package.

That package was added to terminal in the fuchsia.git change at
fxrev.dev/587281 and once that modified version of the "terminal"-based
image is used by fuchsia/engine CI, assuming it was the last blocker,
hopefully the test will now pass in CI.

The test does pass when run from a development environment.

Replace this paragraph with a description of what this PR is changing or adding, and why. Consider including before/after screenshots.

List which issues are fixed by this PR. You must list at least one issue.

If you had to change anything in the flutter/tests repo, include a link to the migration guide as per the breaking change policy.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt. See testing the engine for instructions on
  writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.

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[richkadel]

Resolved in #29565 (woohoo!)