(Attempt to reland #85993)

This reverts commit 2175e64e.

Migrate core devicelab framework to null safety.

This reverts commit 05d55157.

This reverts commit ef2879a4.

Fixes an incorrect cast that caused a build failure.

Landing on red to fix the build.

This adds avoid_dynamic_calls to the list of lints, and fixes all instances where it was violated.

Importantly, this lint is NOT turned on for flutter/packages/test, because those changes are happening in another PR: #84478

* pub global deactivate devtools before installing
* upgrade devtools to latest

This reverts commit 99a947c3.

This reverts commit 714dea5e.

This reverts commit a3893aea.