(Breaking Change) Move some hardcoded pixel values to reusable constants.

* some space formattings

* always use blocks in if-else if a block is used

* format spaces in for and while

* allow multiline if conditions

* fix missing space

* fix some formatting issues

* address review comments

* fix indent

* add trailing commas on list/map/parameters

* add trailing commas on Invocation with nb of arg>1

* add commas for widget containing widgets

* add trailing commas if instantiation contains trailing comma

* revert bad change

Allow heroes to fly across navigators and restrict Cupertino nav bars to per navigator by default (#23322)

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

It was causing problems rolling Flutter into Fuchsia

* re-enable lint unnecessary_const

* remove trailling whitespaces

* remove unnecessary const (after merge)

This reverts commit cc1cf13e.

Put the nav bar padding inside the CustomMultiChildLayout for correct centering and allow custom padding (#19129)

* Surface border parameter in CupertinoSliverNavigationBar (#18152)

* Add tests for CupertinoSliverNavigationBar border

* Remove unused keys, find by descendant

This is not a grand refactor yet, it's just cleaning up what we have
already, so that people who keep using this API (e.g. dialogs) have
something coherent to deal with.

The major changes are that Navigator and NavigatorState have the same
API now, that most of the examples use `<void>` instead of `<Null>`,
that the navigator observer can see replaces, and that the `settings`
is moved from ModalRoute to Route. I also cleaned up some of the API
documentation.

- Add override of border color of CupertinoNavigationBar
- Add background color to CupertinoPageScaffold