PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/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-angular/blob/master/DevelopmentWorkflow.md#running-the-tests
• Tests for the changes are included.

What is the current behavior?

What is the new behavior?

Adds RootLayout to element-registry. This is the changes required for RootLayout to work with Angular (NativeScript/NativeScript#8980). This is dependent on Nativescript's release/8.0.0 branch

Fixes/Implements/Closes #[Issue Number].