See https://github.com/flutter/flutter/issues/9257#issuecomment-550503833

This reverts commit a214b462.

* Add Material Study app Rally to examples

This adds a canRequestFocus and skipTraversal argument to FocusScope and FocusScopeNode, so that a scope can prevent being traversed.

This allows a fix for a problem in the gallery where the focus while traversing the list of items would sometimes appear to disappear, since it would be focusing things that were in the backdrop that were part of the tree, but were not visible.

Related Issues
Fixes #42955

Made the Flutter Gallery use the new ThemeMode property so that it can
use the system's dark/light mode setting by default.

* more ui-as-code

* address review comments

Update the flutter_gallery Slider demo by aligning the text field in the first slider, adding range slider examples (including custom range thumbs), and separating single slider and range slider examples with tabs.

This implements focus and hover handling for Material buttons. It inserts Focus widgets into the tree in order to allow buttons to be focusable via keyboard traversal (a.k.a. TAB traversal), and Listener widgets into the InkWell to allow the detection of hover states for widgets.

Addresses #11344, #1608, and #13264.

Adds the "2D Transformations" demo to the gallery, which shows how to do things such as navigate around a map a la Google Maps, or show a full screen zoomable photo.  The idea is to abstract this code into a first class widget soon.

* fix some formatting issues

* address review comments

* fix indent

* 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

* [Gallery] Fortnightly demo moved from flutter/samples.

* [Gallery] Fortnightly analysis corrections.

* [Gallery] Minor rename.

* [Gallery] Making floats ints.

* [Gallery] Fortnightly minor visual polish.

* [Gallery] Formatting.

* [Gallery] Upping package version for gallery to support fortnightly demo.

* [Gallery] Fortnightly copy correction.

* [Gallery] Fortnightly study polish.

* [Gallery] Fortnightly polish.

* [Gallery] Fortnightly copy correction.

* [Gallery] Fortnightly copy now held in '''.

* [Gallery] Fortnightly comment.

* [Gallery] Updates necessary when flutter_gallery_assets updates.

* [Gallery] Updating macrobenchmarks because we updated flutter_gallery_assets.

* [Gallery] Moving spaces to beginning of copy lines.

* [Gallery] Copy correction.

* [Gallery] Adding tooltip to satisfy smoke test.

* [Gallery] Minor pr feedback.

* [Gallery] Forced upgrade.

* the onStart callback will report the location of the pointer where it wins the gesture arena by default instead of the pointer down location. Fixes all tests related to changing this default value.

This reverts commit 4ec8883b.

We have templates now.

This reverts commit 76a1abd4.

This reverts commit 949cfcf1.

* Future<void> main

* Future<void>.delayed

* prefer_void_to_Null

* address review comments