* Reland "Nnbd widgets (#64672)"

This reverts commit 127e6790.

* remove non-nullable enforcement on AsyncSnapshot

* make data param non-nullable for AsyncSnapshot.withData

* make some Text params non-nullable

This reverts commit e682ec71.

* migrate widget to nullsafety

* remove double blank line after license

* address review comments in actions.dart

* nullable ObjectKey.value

* use local variable oldElement

* make State.build non-nullable

* make State.context non-nullable

* newline at eof

* make ProxyWidget.child non-nullable

* make _InactiveElements.debugContains non-nullable

* make Element.depth non-nullable

* make ProxyElement.build non-nullable

* make StatefulElement.state non-nullable

* remove 'Notice that'

* avoid cast of list in RenderObjectElement.updateChildren

* make IndexedSlot.value non-nullable

* avoid cast of list in MultiChildRenderObjectElement.mount

* make some WidgetsApp parameters non-nullable

* hitTest take non-nullable position

* make ScrollableState.position non-nullable

* use _pixels instead of pixels

* make ViewportOffset.pixels non-nullable

* make param and return type of IndexedWidgetBuilder non-nullable

* unused_import

* make context param non-nullable for Builder in animated_list.dart

* make ScrollMetrics.viewportDimension non-nullable

* make ScrollMetrics.{min,max}ScrollExtent non-nullable

* make _Location.file non-nullable

* _WidgetForTypeTests.createElement throw UnimplementedError

* update _NullWidget.build error message

* make _ShortcutsState.manager non-nullable

* Fix childCount issues for NNBD

* fix childCount computation on web

* increase max value on js side to compute childCount

* make aspect parameter of dependOnInheritedWidgetOfExactType nullable

* merge has{min,max}ScrollExtent into hasScrollExtents

* update focus_manager.dart

* address review comments in icon.dart

* address review comments in image.dart

* address review comments in routes.dart

* address review comments in scroll_activity.dart

* update doc comments

* make UserScrollNotification.direction non-nullable and required

* rename hasScrollExtents to hasContentDimensions

* unnecessary late
Co-authored-by: Ian Hickson <ian@hixie.ch>

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

This reverts commit 0f8c0da0.

smartDashesType and smartQuotesType params for text fields to control iOS's smart punctuation feature.

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs

No code changes, just comments: I spell-checked all the comments in the repo.

This flag controls Android's keyboard suggestions on/off

Use assertions to prevent multiline password fields from being created

In #42533, I disabled the up/down arrows for focus navigation in text fields, but we thought of a better way to do it, so this is that better way.

This change reverts the other change, and instead it tests the context of the node in the action to see if it's an EditableText node. If so, then it doesn't do the navigation action.

This disables the arrow key focus navigation for text fields. This was non-standard behavior for text fields, although it remains useful for other kinds of controls.

Fixes #42259

* add missing trailing commas

* add more missing trailing commas

* add more and more missing trailing commas

Add an autofocus parameter to widgets which use Focus widget internally, and update related docs.

This will allow developers to request that a particular widget be automatically focused when shown.

reland Enable selection by default for password text field and expose api to turn on and off context menu options (#37324)

Revert "reland Enable selection by default for password text field and expose api to turn on and off context menu options (#34676) (#37183)" (#37295)

This reverts commit 7eb09a84.

reland Enable selection by default for password text field and expose api to turn on and off context menu options (#34676) (#37183)

This reverts commit 48c7090f.

Revert "Enable selection by default for password text field and expose api to turn on and off context menu options (#34676)" (#37055)

This reverts commit 0d0af315.