* Refactor of cupertino/material/widgets app

* update docs 

* Update tests for const

This reverts commit 61cf946b.

* Make CupertinoApp and MaterialApp both use WidgetsApp for Navigator

* Make CupertinoApp and MaterialApp const constructors

* Make WidgetsApp routes aware

* Update tests

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

Fixes #21250

Rewrote CupertinoAlertDialog to look nearly identical to an alert dialog in iOS. This includes considerations for blur, translucent white background color, button sizing, gap dividers between buttons, and text scaling layout behavior. (#18381)

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.

This replaces abandoned PR #14824 by @ekbiker, and gives it some love.

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.

* replace child parameter with builder on showDialog

* change builder parameter to WidgetBuilder

* mark child as deprecated and expand documentation to cover this and how builder should be used

* tidy comments and address some feedback

* phrasing

* move space to prev line and add //ignore comments for deprecated member use

* address comments and fix it's its

* update code samples

* adds semicolon to code snippets

This updates the CupertinoAlertDialog to respect text scale factor more properly. Before this, it would scale, but would clip the action buttons at large scales, and would draw in the safe area. It also didn't match the iOS alert because the content didn't scroll. Now it does those properly.

I didn't address the fact that buttons should lay out properly (Issue #14345), but that's probably pretty low priority.

Fixes #12484

* is default

* hit target

* correct test name

* review note

* more widget const constructors

* prefer const constructors

* address review comments

Aggressively apply the const lint.

...now that we have generic methods, their types need to be specified too.

Fixes #7375