In some cases you might want to set a parent(mostly rootView) before _setupAsRootView so that the the view calling _setupAsRootView inherits CSS variables and classes from the parent.
This is especially done in plugins like bottomsheet or dialogs or popover.
The issue is that if you set parent before _setupAsRootView then _addViewToNativeVisualTree will be called which could break things like it does with RadSideDrawer nativescript-community/ui-material-components#462.

This PR fixes that by just preventing _addViewToNativeVisualTree to be called from _setupAsRootView which makes sense to me.

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/NativeScript/blob/master/tools/notes/DevelopmentWorkflow.md#running-unit-tests-application.
• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/tools/notes/WritingUnitTests.md.

What is the current behavior?

What is the new behavior?

Fixes/Implements/Closes #[Issue Number].