* Use `curly_braces_in_flow_control_structures` for `widgets`

* fix comments

* fix comments

* Reland "Fixes zero route transition duration crash (#90461)"

This reverts commit 403c1de5.

* Fix paged base route pop before push finishes crashes

This reverts commit 0eeb026e.

This reverts commit 5fd259be.

This reverts commit d056500b.

This reverts commit 31de052e.

This reverts commit e2490f29.

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.

* Migrate more tests

* fix