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.
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• 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?

There is currently an issue on Svelte Native that's related to HMR removing page elements and throwing exception.
The reason is that even though _removeView unsets page parent, the page still keeps reference of parent using property _frame and parent Frame happens to check that property when trying to dispose entry views in Core.

What is the new behavior?

This change will ensure page won't keep any reference to parent after disposal. Doing so helps avoid calling _removeView multiple times.
More specifically, it ends up meddling with the following check:
https://github.com/NativeScript/NativeScript/blob/main/packages/core/ui/frame/frame-common.ts#L201

Fixes #10361 halfnelson/svelte-native#347