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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?

On Android, the current automationText sets the content description but not the tag. Detox uses the content description as by.label() and a tag as by.id(). There is currently no built-in way to use by.id() (on Android at least).

What is the new behavior?

Implements #8943.

Adds the testID property which uses setTag() on Android and accessibilityIdentifier on iOS.

testID can be used for Detox's by.id() and automationText can be used for Detox's by.label().