devtools

018cd611 - Fix issue where first build of the VM Tools status bar would cause a null pointer exception (#2905)

Fix issue where first build of the VM Tools status bar would cause a null pointer exception (#2905) `VMDeveloperToolsScreen` exposes a `ValueListenable` provided by the `VMDeveloperToolsController` in order to control the visibility of the isolate selector. Given that `VMDeveloperToolsScreen.showIsolateSelector` can be invoked before the static controller in `_VMDeveloperToolsScreenState` is initialized, a null pointer exception was being thrown when first building the VM Tools screen. This change updates `DevToolsScreen` to take either a `createController` callback or a pre-instantiated `controller`, allowing for the same instance of `VMDeveloperToolsController` to be used by `VMDeveloperToolsScreen` while also being exposed via `Provider`.