[Accessibility API] Add implementation for isRequired API

This CL will implement the API defined here:
go/required-fields-api-change-design-proposal

Flag: android.view.accessibility.a11y_is_required_api
Test: Unit Tests
Bug: 362784787
Change-Id: I7a6fc2cdc96c7d2279141092fa6f4b0a7f8789fa
3 files changed