Updating SDK and package versions now that alpha has been rolled to 0.0.20

Includes:
flutter/engine#4442
flutter/engine#4445
flutter/engine#4444
flutter/engine#4448 (reverts flutter/engine#4444)
flutter/engine#4447

We thought it would be OK to call the create command offline-only, but it turns out that isn't a great idea because not all of the create template dependencies are cached by running flutter_tool.

This PR makes it go online by default when running pub get after creating a project, and adds an "--offline" flag to the create command so that offline users can use it offline if their cache is warm.

See https://github.com/flutter/flutter/issues/11907 and https://github.com/flutter/engine/pull/4411

* Expose textAlign on TextFormField

Fixes #11404

* Added name to AUTHORS

* Added a test for TextFormWidget's textAlign

* Fix for incorrect transparent -> DividerColor animation for ExpansionTile

* Add comments and tests. Fix background color too.

* Fix analyzer warnings

Includes:
flutter/engine#4429
flutter/engine#4415
flutter/engine#4431
flutter/engine#4432
flutter/engine#4401
flutter/engine#4434
flutter/engine#4435
flutter/engine#4436

Removes bottom padding from the child AppBar in SliverAppBar. Scaffold
already does this for its own app bars, but sliver app bars in the body
should also apply the bottom padding removal.

Fixes flutter/flutter#13458

...instead of the engine.

This removes the FLUTTER_TEST_ARGS environment variable handling.

In order to allow offline usage of the create command we need to be able to tell pub not to try and contact the server to see if new versions are available. Since all the versions that create could want are pinned, it shouldn't need to check for new versions.

Also:

* Remove find.byIcon since it's identical to find.icon. (I sent mail to flutter-dev about this.)

* Fix IconData's operator== and hashCode, which had not been updated when we added fields.

* Add the byTooltip finder to the list of suggested finders.

* Make the suggested Key finder prettier.

* make time picker accessible

* use new CustomPaint a11y API

* flutter_localizations tests; use bigger distance delta

* fix am/pm control; selected values

* fix translations; remove @mustCallSuper in describeSemanticsConfiguration

* exclude AM/PM announcement from iOS as on iOS the label is read back automatically

Let translucent Cupertino bars have its scaffold children automatically pad their heights - second try (#13440)

* Let translucent Cupertino bars have its scaffold children automatically pad their heights (#13194)

* Let lists automatically add sliver padding from media query. Translucent nav and tab bars leave behind media query paddings in scaffolds.

* tests

* const lint

* Rename base abstract class to generalized ObstructingPreferredSizeWidget

* review

* More docs and comments from #13317

* Update dartdoc to 0.15.0+1 for Flutter.

* Minimize change

Includes:
flutter/engine#4427
flutter/engine#4428

Includes:
flutter/engine#4422 (Dart SDK roll)

* Remove unnecessary error message

* Add AUTHOR

Updates scaffold to expose bottom padding to the associated
BottonNavigationBar (if present). BottomNavigationBar is now responsible
for adjusting itself to account for bottom padding.

This change is necessary to support the updated BottomNavigationBar
layout for the iPhone X.

* Remove MediaQuery padding for various PopupRoutes that don't extend to the edge of the screen

* bottom sheet doesn't actually need handling. Scaffold does it already. Add test for others.

Now that keyboard height is modelled as a (bottom) view inset, migrate
scaffold bottom resizing to use view insets instead of bottom padding,
which, after an engine roll, will only be used for safe areas.

Until the aforementioned engine roll, the keyboard height is still
included in both bottom padding and view insets. As such
resizeToAvoidBottomPadding still drives bottom padding removal until
that roll lands.

Renames _ScaffoldLayout.bottomPadding to bottomViewInset

Also adds a TODO that should have landed with flutter/flutter#13423.

This patch contains no framework changes.

This change adjusts a test bottom navigation bar height to be greater
than the media bottom padding.

This change is pre-factoring to clarify diffs in an upcoming change that
will expose bottom padding to the bottom navigation bar in order to
allow it to visually adapt its appearance in the presence of bottom
padding such as thatexposed for the iPhone X home screen indicator.
Since the bottom padding was previously greater than the height of the
bottom navigation bar, the height of insideBottomNavigation bar was
driven to 0 when padding is exposed.

This allows the scheduler library to depend on the services library
and the painting library to depend on the scheduler library without
the services library having to depend on the scheduler library.

While I was at it I also cleaned up some of the binding logic: the
licenses logic can now be overridden (and the test library does so),
and the image cache can now be overridden as well.

This reverts commit 9315a79b.

There is an unfortunate interaction with verifyThenRunCommand