Fixes #24158

Fixes flutter/flutter#22062

Upgraded Scaffold example to an application example.

* Revert "Make host app test actually test host app (#24131)"

This reverts commit 27293857.

* Revert "Roll engine 5646e86a6f44..2584816d78a3 (2 commits) (#24197)"

This reverts commit 846a5eea.

* Make host app test actually test host app

* mark updated test as flaky

https://github.com/flutter/engine/compare/5646e86a6f44...2584816d78a3

git log 5646e86a6f44..2584816d78a3 --no-merges --oneline
2584816d7 Roll Dart version to f9ebf2129732fd2b606286fdf58e500384b8a0bc (flutter/engine#6812)
9669aeb95 Roll src/third_party/skia 06a477c3300d..ef4709b7850d (31 commits) (flutter/engine#6811)


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* Re-order platform_integration to be more featured
* Remove flutter_goldens_client
* Fix snippet precompilation to always run `pub get` and
  to detect snapshot failure

To see if it stops the Cirrus crashing