Add support for creating an "empty" project

[gspencergoog]

Flutter recently added an option to flutter create to create an empty project that doesn't have any comments, the code is just a hello world instead of the counter app, and there's no test directory. The flag is --empty.

It would be nice to add the option to the IntelliJ extension to allow people to create an empty project instead of one that has the counter app in it. I'm not sure how that should manifest, it could either be an option setting that modifies the "Flutter: New Project" dialog, or an additional "Flutter: New Empty Project" dialog, I'm not sure which is more appropriate (maybe the former?).

For context, see this comment, the PR that added the flag: flutter/flutter#113873, and the related VSCode feature request.

[stevemessick]

Thanks @gspencergoog for the suggestion. I also need to add the plugin_ffi template. I'll probably just add both to the existing drop-down list, then see if I need to change the command-creation code.

Note-to-self: remember to check the SDK version when generating the drop-down list content. This new flag is currently only in the master branch, I believe.