fix(core): RootLayout view and shade cover should animate in parallel

[CatchABus]

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?

RootLayout view and shade cover don't animate in parallel.

What is the new behavior?

This fixes animation problems caused by #10228, makes few of checks more obvious, and adds a bit more of a missing promise functionality for method openShadeCover.

BREAKING CHANGES:

Method openShadeCover return type changes from void to Promise<void>.

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✅ Successfully ran 2 targets

• nx run-many --target=test --configuration=ci --projects=core
• nx run webpack5:build

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[NathanWalker]

This is looking good @CatchABus thanks for handling 🤗