adjust upgrade command

Fix fullscreen dialog gallery example

More elaborate exceptions.

AnimatedOpacity

This provides an easy way to do implicit opacity transitions.

The elaboration will continue until morale improves.

Specific exceptions considered here:

 - size setter checking when you set the size
 - layout verifying that you do set the size
 - hitTest verifying that you aren't dirty and have a size
 - flex complaining about canFlex

Adds constants for FractionalOffsets

Adds some names for common FractionalOffset values.

Pointer events should pass buttons through

Fixes #2899

Remove two `flutter analyze` regular expressions

Update test.sh

fix an exception from flutter doctor

We can work around these in code rather than by post-processing the analyzer
output.

[driver] propagate exit code from package:test

Driver returns exit code 0 even when tests fail. This commit fixes it by
propagating the exit code set by `package:test`.

Use --packages rather than --package-root

The .packages file is replacing the packages directory of symlinks.

ChildView throws exceptions outside MojoShell

Rename debugOwner to debugCreator

Fixes #2940

`flutter upgrade` needed twice if sky_services dependencies change

Now we run `flutter --version` to update our local cache of packages before
running `pub upgrade`, which reads from that cache.

Fixes #2953

We're missing a null check.

Fixes #2949

Added a Form widget to manage multiple Input widgets.

Add all variants of the Roboto font as assets to Material Design apps

Improve _AnimatedEvaluation.toString

upgrade to test 0.12.13

Update to Dart SDK 1.15.0

...and fix a typo in a setState assert message.

toStrings for Animations and Animatables