Do not throw when resolving a local engine if the .packages map does not include the flutter package (#5519)

TBR

Alternative PowerShell script. Fix missing pop in BAT file (in case of fatal error). Exit gracefully. Force SDK Path. (#5484)

The type of rejects should be List<dynamic> to match the type that
DragTarget expects. Since the function doesn't use rejects anyway,
there's no need to tighten the type.

Fixes one of the strong_mode_static_type_error errors that is currently
being ignored.

Added a widget that implicitly animates the size of it child.

Added a widget that automaitcally rotates the expansion icon and
offers a callback interface that captures presses.

Using IconButton inside of a bigger Material before would result
in having a hit box as large as the whole Material. This commit
constrains the size of the hit box and splashes to the default
diameter of a splash.

Fixes https://github.com/flutter/flutter/issues/5462

@mpcomplete

Fixes https://github.com/flutter/flutter/issues/5468

Currently, we just treat Fuchsia as TargetPlatform.android, but we might
want to do something more sophisticated in the future.

These tests should hit some previously untested lines.

This commit changes MergeableMaterial to include a flag that
specifies whether connected Material slices should have dividers
between them.

This will ensure cleanup of any files that existed in previous versions of
the artifacts but have since been removed

* use transparent android launcher icons

* revert stocks icons

* Build sky_engine Dart SDK summary bundle on FlutterEngine.download().

* Tweaks for Devon comments.

* Tweaks for Phil comments.

Turns out that previously we weren't updating the clip if the layout
didn't change, even if the delegate was different.

I accidentally checked in this as true in my patch improving this feature.

* new launcher icons for android

* two more sizes for android launcher icons

We have so many render objects going on these days that showing every
box that gets an event just makes the screen blue. This limits it down
to only the ones that are actually doing something with the events.