Duplicate tests that use examples from qtdeclarative

Moving examples from qtdeclarative to qtdoc broke tests that operate
on the example sources. This patch duplicates those tests and the
documentation snippets that serve as test data to reestablish test
coverage.

Task-number: QTBUG-69383
Change-Id: I31fd1729f794081a11844be9c27ed4f9a8a5ce73
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>