AdoptAWidget - Progress indicator (#69498)

* Add examples for LinearProgressIndicator

* Add examples for CircularProgressIndicator

* Change name Linear  -> Circular

* Remove unnecessary changes

* Add images to docs

* Fix semi-colon bugs

* Fix trailing spaces

* Fix more semicolon bugs

* Remove imports in docs

* Remove error causing line breaks

* Add ticker providers

* Add more ticker providers

* Remove assets and combine samples

* Removed 6 samples

* Remove unnecessary animation

Co-authored-by: John Ryan <ryjohn@google.com>

* Remove unnecessary animation

Co-authored-by: John Ryan <ryjohn@google.com>

* Use material theme

Co-authored-by: John Ryan <ryjohn@google.com>

* Apply suggestions from code review

Co-authored-by: John Ryan <ryjohn@google.com>