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• 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.
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• All existing tests are passing: https://github.com/NativeScript/NativeScript/blob/master/DevelopmentWorkflow.md#running-unit-tests.
• Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/WritingUnitTests.md.

What is the current behavior?

The only way to schedule a macrotask is by using setTimeout, and even that isn't a guaranteed to be executed immediately (ready: before frame) on iOS.

Here's an example (for some reason playground is not saving the new version, so comment the last setTimeout of home.component.ts` or you'll freeze for a few seconds at the home page): https://play.nativescript.org/?template=play-ng&id=B4UY5b&v=2

What is the new behavior?

Defines a proper scheduler for macroTasks by queuing a task on the main thread) that will run after all microTasks have ran. requestAnimationFrame is now in a macroTask to mimic web behavior (this is necessary because angular will use requestAnimationFrame to schedule it's change detection).

Looking for input in error handling and if we should schedule multiple tasks instead of scheduling one and iterating through the callbacks.