Use super-initializer parameter in live templates

[MrLightful]

To avoid having to manually pass each parameter into the super invocation of a constructor, you can use super-initializer parameters to forward parameters to the specified or default superclass constructor. This produces cleaner classes.

This PR thus updates live templates to use them instead.

Language Tour | Dart -- Constructors
Language Tour | Dart -- Design

Addresses: #6071

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[stevemessick]

Thanks for the PR. Unfortunately, this won't work for older versions of the Dart SDK. There are many projects that have not migrated to null-safety yet, so they are still using Flutter 2.12 or so. This change requires Flutter 3.0 or newer. Also, we don't edit the XML file; it is generated (see below).

If you want to make this change, modify FlutterLiveTemplatesProvider to check the Flutter SDK version and return a file that works for that version. Unfortunately, getting the SDK version will be difficult, as it depends on the current Project. There may be multiple projects open and each could have its own SDK version. I think it can be done using the IntelliJ WindowManager API. (You'd need to find the top-most JFrame then query it for its project.) You'd also need to do some work in the tool/plugin plugin-management tool. It has a generate command that generates the live template file from the templates (*.txt). It would need to be extended to generate both forms.

Ideally, we'd ask the Dart analysis server to provide the live templates. It knows the SDK version so could provide the proper form. There's been some talk about adding that feature to the LSP API, but the Flutter plugin does not use LSP, so that won't actually help us. Unless we hook up the LSP version, too, which isn't on anyone's radar currently.

[stevemessick]

@romatallinn Do you plan to do any more work on this PR? If not, I'll close it.