Add the `DashTool` owner in the dartdocs for each for the event constructors

[eliasyishak]

We should have some information in the dartdoc so that it is easy to tell which DashTool is the "owner" of that event.

For example, you would have to dig through the code to understand who the owner is between Event.commandExecuted and Event.commandUsageValues

  /// An event that reports when the code size measurement is run
  /// via `--analyze-size`.
  ///
  /// Tool owner: flutter-tool   <---- add this
  ///
  /// [platform] - string identifier for which platform was run "ios", "apk",
  ///   "aab", etc.
  Event.codeSizeAnalysis({required String platform})
      : eventName = DashEvent.codeSizeAnalysis,
        eventData = {
          'platform': platform,
        };