(Attempt to reland #85993)

This reverts commit 2175e64e.

Migrate core devicelab framework to null safety.

This reverts commit 0c9781e3.

This reverts commit 93fb2586.

This reverts commit 297c7b5c.

* preserve detailFiles entry in TaskResult JSON

Remove devicelab specific code for shutting down gradle daemon, add --android-gradle-daemon option to build/run/drive`. Avoids need for un-tested devicelab specific handler. There are also some feature requests for this, so 2 birds one stone.

Example:

flutter build apk --no-android-gradle-daemon will pass --no-daemon on to gradle

This reverts commit ddab72e7.

Remove devicelab specific code for shutting down gradle daemon, add --android-gradle-daemon option to build/run/drive`. Avoids need for un-tested devicelab specific handler. There are also some feature requests for this, so 2 birds one stone.

Example:

flutter build apk --no-android-gradle-daemon will pass --no-daemon on to gradle

--use-application-binary allows running with an already built APK. This can be useful for speeding up CI test cases, or in our case eventually supporting some sort of build server. Demonstrate that this works by updating the old gallery test to use it. Fixes #56604
Co-authored-by: Jenn Magder <magder@google.com>

* report failure for semantics test

* bug fix

Move Flutter Gallery to dev/integration_tests/ as it is an older copy used only for testing. The current version of the Flutter Gallery now lives in https://github.com/flutter/gallery.