* Remove deprecated kind in GestureRecognizer et al

* Fix null case

* DragTarget part 1.

[WIP] Change GestureRecognizer. Sorry.

[WIP] Move from GestureRecognizer to MultiDragGestureRecognizer.

Make it a `Set<int>?`

Get bitwise operations working.

Fix test. Rename to allowedInputPointers.

Convert into a builder.

Improve code with default funciton.

Refactor everything again.

Rename to buttonEventFilter.

Use static function.

Fix analyzer.

Fix private reference.

Use // in private method.

* Fix Renzo request.

* Add `allowedButtonsFilter` everywhere.

* Refactor monoDrag for multi pointer support.

* Fix tests?

* Change default to always true.

* Fix PR comments.

* Completely refactor long press.

* Add forgotten class.

* Revert "Completely refactor long press."

This reverts commit 5038e8603e250e8c928b0f1754fb794b7b75738b.

* Add default value to LongPress

* Refactor doubleTap.

* Relax double tap.

* Write comment in LongPress.

* Use template.

This is a re-application of https://github.com/flutter/flutter/pull/81884,
but with https://github.com/flutter/flutter/pull/82834 landed first.

Fixes https://github.com/flutter/flutter/issues/81883

This reverts commit e88a387b.

* Gesture recognizer cleanup

1) Make OneSequenceGestureRecognizer.addAllowedPointer()
   call startTrackingPointer(), and change subclasses to
   call super.addAllowedPointer() in place of manually
   calling startTrackingPointer().
2) Fix addAllowedPointer overrides to take PointerDownEvent
   where some were taking PointerEvent.
3) Add API documentation to OneSequenceGestureRecognizer
4) Make the following fields in OneSequenceGestureRecognizer
   private with public getters instead of publicly writable:
   `state`, `primaryPointer`, and `initialPosition`.
5) Clean up gesture recognizer state in
   OneSequenceGestureRecognizer.didStopTrackingLastPointer.

Fixes #81883

* add language version 2.8 in packages/flutter

* enable non-nullable analyzer flag

* 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

* some space formattings

* always use blocks in if-else if a block is used

* format spaces in for and while

* allow multiline if conditions

* fix missing space

This recognizer can be passed in AndroidView's gesureRecognizers when we
want all touch events in the view bounds to be immediately dispatched
to the Android view.