This creates a custom dartdoc tool that will generate snippet blocks in our API docs that allow the user to copy easily to the clipboard, and will also embed the snippet code into a template to show it in a larger context with an app.
This PR adds the snippet tool, a template, and a couple of HTML skeleton files, one for snippets that are designed to be in an application setting, and one where it simply puts a nice container around existing snippets, making them easier to copy to the clipboard.
* Split analysis steps out of dev/bots/test.dart into dev/bots/analyze.dart.
This allows to run analysis step with command line arguments that are only applicable to flutter analyze(like --dart-sdk, needed for dart-flutter-engine head-head-head bot).
* Add forgotten dev/bots/analyze.dart
* Refactor common code from analyze.dart and test.dart into run_command.dart
* Remove comments, add header
