* Use `curly_braces_in_flow_control_structures` for `material`

* include test/material

* add back removed comments

Update samples to use repo analysis options, Fix sample templates and a ton of analyzer issues (#77868)

This reverts commit 79d0358e.

Adds Navigator.maybeOf to replace calling Navigator.of(context, nullOk: true), and removes the nullOk parameter. Also changes Navigator.of to return a non-nullable value, and removes many (120!) instances of the ! operator, reducing the possible places where a null dereference could occur.