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• 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.
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• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/tools/notes/WritingUnitTests.md.

What is the current behavior?

When it comes to reusable views, it seems that view box shadow is not removed when view gets removed from view tree.
That is because shadow layer belongs to parent and we rely on disposeNativeView to cleanup shadows but that doesn't seem to be the right approach.

What is the new behavior?

Add/remove shadows along with view, regardless of being reusable or not. It's also a good replacement for my previous PR.