* Adding outlines to text fields

* Added new ButtonBarTheme to replace the deprecated ButtonTheme.bar method.

* Responding to PR feedback.

* [Material] Create material Banner component (#36880)

This PR creates a new material widget for the Banner component. This includes a theme as well. This widget can be dropped into any application, ideally at the top of a listview or scrollview.

(cherry picked from commit 35b6d668)

Removed the use of ButtonTheme.bar in the Banner implementation.

* Updated documentation from PR review comments.

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

Fix the Expansion Panel flutter_gallery demo by wrapping the Slider in a padded Container so that the value indicator does not get clipped.

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.

Corects a bnuch of typeos throuhgout teh Fluter codebsae.

Made use of the `misspell` tool:
https://github.com/client9/misspell

Removed the GestureDetector from the modal bottom sheet that dismissed it on tap and updated several tests to accommodate this change.

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.

* make immutables const

* add text style params

* add icon theme params

* Added tests 

* Re-enable const

- Fixed the bug where CupertinoRefreshControl doesn't work in the gallery demo on Android.
- Updated documentation on CupertinoRefreshControl
- Added comments to the gallery demo
- Added concrete examples to ScrollPhysics

This PR introduces a number of changes and improvements to snack bars. This includes the ability to specify:

floating style of snack bars that adhere to the updated Material spec
elevation and shape on the SnackBar itself instead of relying on fixed values
a snackBarTheme as part of ThemeData which allows you to customize all of the above on an app-wide level.
This PR is includes the changes from #21484 as well as additional fixes and modifications. Thanks to @NikoYuwono for providing these changes and getting this off the ground!

Adds an adaptive constructor for the Material Slider. An adaptive widget is one that renders itself as Material on Android, and Cupertino on iOS. This work is based off of a similar feature on Switches: bbb080b3#diff-fe2bb980c6207699cbf45538fe927afa.

The motivation for this change is that we should provide adaptive constructors for as many widgets as necessary in the Material library. In Material, it is suggested that the slider is an iOS-style slider.

Small usability fixes for pan and zoom demo. Title and instruction dialog.

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.

The @flutterio account now just directs people to @FlutterDev:

https://twitter.com/flutterio

* 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

* fix indentof statements in BlockFunctionBody

* fix indentof statements in BlockFunctionBody in tests