The remaining uses of this pattern were all due to wanting to have
the child's slot when `Element.forgetChild()` was called. However,
when that method is called, the child's `slot` value is still valid
in the context of the parent, so the uses can just use `child.slot`.

This is the final round of cleanup from the fallout of #63269

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

This reverts commit 8de07d55.

This reverts commit d9882263.

Unrevert of paste button hides when nothing to paste

This reverts commit d5634982.

Unreverts #54902 with fixes for a failing integration test.

This reverts commit 053c3881.

Adds the ability for the iOS text selection menu to handle items that are too wide for the screen.

This reverts commit 2132a0c7.

This reverts commit 69080e07.

This normalizes all of the "See also" blocks in comments so that they conform in style.

They all look like this now:

  /// See also:
  ///
  ///  * [MyFavoriteWidget], because it's cool.
  class Foo {}

I removed some useless "See also" blocks, and added commentary to ones that were just "bare" references.

This is my penance for adding so many bullets that are "-" instead of "*". :-)

* 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

Fix bug where selection menu appeared at top of screen for multiline inputs.

The text selection handles now feel a lot more responsive, and their implementation was cleaned up a bit.

* 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

* Fix internationalization issues with cupertinoTextSelectionControls

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* Fixes resulting from audit of issues links

I looked at every link to GitHub in our repo. For cases where we had a TODO that was waiting for a bug to be fixed, and the bug has now been fixed, I applied the pending change. For cases where the link was out of date, I updated the link.

* Update run_test.dart

skip this test again since it failed on linux and macos bots