Drop Pub Transformers

As of angular: 5.0.0-alpha+5 the pub transformer has been removed in favor of
code generation through package build. To build your project with
build_runner:

1. Add two dev dependencies to your pubspec.yaml file:

dev_dependencies:
  build_runner: ^0.7.8
  build_web_compilers: ^0.2.1

2. Run pub get on your package.
3. Build your package:

pub run build_runner build

Or run a local development server with a file watcher and incremental
rebuilds:

pub run build_runner serve

Updates

• Material Dialog: Add mixin for bottom border on header.
• Material Drawer: Add mixin for width.
• Material Input:
  • Extend the style rules applied on input[type=text] to cover the hover and
    focus states.
  • Add mixin padding.
• Material Popup:
  • Guard against container = null in PopupHierarchy.onTriggersOutside().
  • Increase the animation speed according to material specs.
• Material Radio: Migrate away from QueryList.
• Material Tree:
  • Add an option to material tree group to render a "View more" link for
    hidden options.
  • Migrate away from QueryList.
• Scorecard: Only update selected state if the scorecard is selectable.
• Use a reified Provider for defaultPopupPositions.
• Add IntersectionObserver bindings & onIntersection stream to ScrollHost.
• Add materialNumberDirectives to MaterialDirectives list.
• Preparation for Angular changing the default value of
  visibility: Visibility.local.
• Cleanup type warnings and other Dart 2 fixes.
• Update documentation.