Add  typically used parameter name to the builder used in layout_builder

* dart fix --apply

* manual fixes

* fixes for incomming linter

* + todo

* todo format fix

* justify ignore

* --

* Use `curly_braces_in_flow_control_structures` for `widgets`

* fix comments

* fix comments

This does a cleanup of the examples, removing all of the "section" markers and extra comments that we don't need anymore now that the samples are no longer in the source code. It also removes the --template arguments from the {@tool dartpad} and {@tool sample} directives, since those are no longer used. It converts two examples that I discovered were still embedded into linked examples in the examples folder.

I didn't delete the templates from the snippets config folder yet, because there are still embedded samples in the dart:ui package from the engine that use them. Once dart:ui no longer uses the templates, they can be removed.

I bumped the version of the snippets package to pick up a change that allows removal of the --template argument.

This extracts the sample code out from the API doc comments, and places them in separate files on disk, allowing running of the examples locally, testing them, and building of slightly larger examples.

Update samples to use repo analysis options, Fix sample templates and a ton of analyzer issues (#77868)

* 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>

This reverts commit ce40de69.

(this re-applies #64189 by reverting #64249)

This reverts commit 21cfed34.

* (insert|move|remove)ChildRenderObject Deprecation: Step 1

This deprecates the following methods:

* RenderObjectElement.insertChildRenderObject
* RenderObjectElement.moveChildRenderObject
* RenderObjectElement.removeChildRenderObject

...and replaces them with the following methods:

* RenderObjectElement.insertRenderObjectChild
* RenderObjectElement.moveRenderObjectChild
* RenderObjectElement.removeRenderObjectChild

The reason for the deprecation is to provide the `oldSlot` argument to
the `moveRenderObjectChild` method (such an argument was missing from
the now-deprecated `moveChildRenderObject` method) and the `slot`
argument to the `removeRenderObjectChild` method (such an argument was
missing from the now-deprecated `removeChildRenderObject` method). While
no argument was added to `insertRenderObjectChild`, the name change (and
corresponding deprecation) was made to maintain naming parity with the
other two methods.

This initial step does not update or remove any of the `slotToChild`
patterns that exist in the framework. This work is being separated
into two commits in case something needs to be reverted to minimize
the scope of each commit.

See https://github.com/flutter/flutter/issues/63269 for more info

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

Avoid calling `builder` in `ConstrainedLayoutBuilder` when layout constraints are the same.

[Design doc](flutter.dev/go/layout-builder-optimization).

## Related Issues

Fixes https://github.com/flutter/flutter/issues/6469

This reverts commit 2132a0c7.

This reverts commit 69080e07.