Revert "Merge branch 'master' into master"

This reverts commit e3a03c04, reversing
changes made to 64749826.

* Composite physical layers even if elevation is 0

This reverts commit 803b15e0.

Reland composite physical layers and update tests

This reverts commit 58fb1832.

* Always composite PhysicalModels
* Update tests to check layer tree instead of canvas for Physical shadows

* 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

This PR does two things:

- It allows BottomAppBar to have a custom shape even when it doesn't
  have a notch.

- It adds AutomaticNotchedShape, an adapter from ShapeBorder to
  NotchedShape.

* 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

Setting the default clip behavior made bottom app bar to no longer clip
its children.
With this parameter users could opt-in to clipping.

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.

Move the notch computation from the FAB to the BAB.

The notch in the BAB (bottom action bar) for the FAB (floating action button) was previously kept as part of the FAB's implementation. This was done to keep the shape of the FAB and the shape of the notch coupled.
That approach resulted in a somewhat complex and 'non Fluttery' mechanism for propagating the notch computation from the FAB to the BAB.

This CL uncouples the FAB and the notch computation.
With the new API the BAB computes its overall shape including the notch using a NotchedShape delegate.

This includes multiple breaking changes:
  * Scaffold.setFloatingActionButtonNotchFor is deleted.
  * The ComputeNotch type is deleted.
  * The hasNotch property of BottomAppBar is deleted.
  * The notchMargin property of FloatingActionButton is deleted.

Quick migration guide from the previous API:

| Previous API | New API |
| ------------------|-------------|
| BottomAppBar(hasNotch: false) | BottomAppBar() |
| Using a FloatingActionButton with: BottomAppBar() / BottomAppBar(hasNotch: true) | BottomAppBar(shape: CircularNotchedRectangle()) |
| Scaffold.setFloatingActionButtonNotchFor(..) | No longer supported |

The downcast was crashing when toggling hasNotch for BottomAppBar.