Bug fix: allow to create ViewTranslationRequest for virtual AutofillId.

1. We provide virtual child list to View#onCreateTranslationRequests
but we don't provide a method to allow developers to create
ViewTranslationRequest for virtual AutofillId. Add a builder
constructor to allow developer to use it for virtual AutofillId.
2. Fix some comments in ag/13982294(e1b23cd4)

Bug: 177789967
Test: manual on sample app
Test: atest CtsTranslationTestCases

Change-Id: I63e914b888b23cdb7a5169fc6931be93625ca8e4