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

This reverts commit 80f80ab0.

For G3 Roll:

* Revert "MaterialButton must honor its minWidth and height parameters (#22919)"

This reverts commit a0233233.

* Revert "Update uses of ButtonTheme.bar: pass along the current Theme's colorScheme (#22827)"

This reverts commit 655bf6a2.

* Revert "ButtonTheme.of().colorScheme defers to Theme (#22880)"

This reverts commit a590940e.

* Revert "Bring TextTheme into alignment with the current Material spec (#22330)"

This reverts commit 8bfb4b3e.

* Revert "Added ColorScheme, updated ThemeData, ButtonTheme, material buttons (#22013)"

This reverts commit eea3465a.

* Manual adjustments to fix reversion issues.

* Update uses of ButtonTheme.bar

* updated gallery themes

* Remove unnecessary const

Fixes #22789

Introduce an overall material "color scheme" and to make it possible to redefine how a component's visual properties bind to the color scheme and to the existing material Theme.