vulkan_glfw validation layer logging

[jwinarske]

This PR enables printing validation output when the Vulkan validation layer is enabled. Without this change no messages are printed which provides a false positive for the Vulkan Embedder API health.

List which issues are fixed by this PR. You must list at least one issue.
flutter/flutter#153663

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cc @chinmaygarde

Fixes flutter/flutter#153663

[flutter-dashboard]

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[jwinarske]

@chinmaygarde I updated the run.sh to use the glfw main.dart; it was commented out prior, and I just pushed change to make it compatible with the GPU test I recently added to glfw main.dart. So it's ready to merge.