* Revert "Revert "Improve performance of collectAllElements (#68065)" (#68207)"

This reverts commit 46ff57d6.

* use fewer elements for benchmark

[devicelab] allow the devicelab to take a screenshot if the iOS connection fails with FLUTTER_IOS_SCREENSHOT_ON_CONNECTION_FAILURE (#68156)

More attempts to remote diagnose the issues in the iOS devicelab

Migrate yet even more widget framework tests to null safety.

This reverts commit d962c8f2.

This crash affects anyone using flutter, so move it into the tool where it can be tested and documented. Ensure it works on windows devicelab too.

This reverts commit 6aa8447a.

This reverts commit 8ba5732c.

* NNBD widget test migration