`showDialog()` and `showGeneralDialog()` were allowing transparent
colors but then triggering an assertion down the stack while building
the modal barrier. The assertion existed to keep from animating from
transparent to transparent, but there's no need for the assertion,
since we can just treat the transparent case as the same as the null
case -- no animation necessary.

The function passes most of its arguments through to
`_DialogRoute`, but it wasn't providing the default
values that `_DialogRoute` was, causing it to override
the defaults will null values.

* Add material page, cupertino page, and transition page classes

* update

* update comments

* fix test

* addressing comments

* make page getter private

* Add semantics sort key for modal scope and modal barrier

* fix test

* fix test

* fix test

* fix space

* fix more tests

* addressing comments

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

When Focus.unfocus is called, the caller usually just thinks about wanting to remove focus from the node, but really, unfocus is a request to automatically pass the focus to another (hopefully useful) node.

This PR removes the focusPrevious flag from unfocus, and replaces it with a disposition enum that indicates where the focus should go from here.

The other value of the UnfocusDisposition enum is UnfocusDisposition.scope.

UnfocusDisposition.previouslyFocusedChild is closest to what focusPrevious used to do: focus the nearest enclosing scope and use its focusedChild field to walk down the tree, finding the leaf focusedChild. This PR modifies it slightly so that it walks up to the nearest focusable enclosing scope before trying to focus the children. This change addresses #48903

A new mode: UnfocusDisposition.scope will focus the nearest focusable enclosing scope of this node without trying to use the FocusScopeNode.focusedChild value to descend to the leaf focused child. This is useful as a default for both text field finalization and for what happens when canRequestFocus is set to false. It allows the scope to stay focused so that nextFocus/previousFocus still work as expected, but removes the focus from primary focus.

In addition to those changes, unfocus called on a FocuScope that wasn't the primary focus used to unfocus the primary focus instead. I removed that behavior, since it was buggy: if the primary focus was inside of a child scope, and you called unfocus on the parent scope, then the child scope could have focused another of its children instead, leaving the scope that you called unfocus on with hasFocus returning true still. If you want to remove the focus from the primary focus instead of the scope, that's easy enough to do: just call primaryFocus.unfocus().

Fixes #48903

Fixes the focus handling when popping pages so that when multiple pages are popped, the focus doesn't try to focus the interstitial pages.

Navigator 2.0: Refactor the imperative api to continue working in the new navigation system (#44930)

[a11y] Make sure RenderFractionalTranslation updates its semantics after the translation field is set (#48985)

* Implement reverseTransitionDuration in TransitionRoute

* 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

This fixes a problem with reparenting of focus nodes where it would remove the node from the scope's focused children when reparented, even if it was being reparented to another place under the same scope. This only occurred if the scope in question didn't have focus.

This caused nodes to not get autofocused when they were a child of another node within the scope, and were reparented, and then the scope was given focus (as when a route is pushed).

This keeps the node in the scope's child list where it was if the node is reparented under a parent within the same scope.

- Added a test that tries to autofocus a TextField when the route is pushed and there is another 
  FocusNode above the text field. This was how this was first noticed: the autofocus got ignored in 
  this configuration.

- Added a test to focus_manager_test that tests for the specific case of reparenting a node when 
  it's in the focused children of the scope.

This reverts commit 0f2254a5.

This PR changes ModalRoute so that, when the route on top of it is popped, it requests to focus on the last focus.

* 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

* Revert "Revert "make LocalHistoryRoute a proper super-mixin (#23382)" (#23430)"

This reverts commit 3bbb3082.

This relands the LocalHistoryRoute change. The analyzer bug has been fixed.

* mark dartdocs as flaky

This reverts commit a3e0b0ae.

This change broke the analyzer during the dartdoc step.

* Future<void> main

* Future<void>.delayed

* prefer_void_to_Null

* address review comments

* 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)