Use super parameters in snippets

[guidezpl]

Is your feature request related to a problem? Please describe.
Feature: dart-lang/language#1855, Flutter repo work: flutter/flutter#100575

Describe the solution you'd like
Tweak the snippets to adopt this feature

[DanTup]

@bwilkerson for code generated by the server (for ex. snippets), should super parameters be used whenever supported, or only if the lint is also enabled?

[bwilkerson]

I think it's reasonable for snippets to make use of any valid language feature that makes the generated code better.

I think that it's reasonable to not produce some style of code when there's a lint that prohibits it (that is, to allow lints to reduce the set of valid language features), but I don't think we want to require users to "enable" new language features before we start producing them in generated code. Or, at least, we don't want to require them to enable it again; they already had to opt in once by increasing the minimum SDK version.

[goderbauer]

+1 I think if the package has a lower SDK bound of at least 2.17.0-0 (indicating that super params are supported) the macros should use them.

[DanTup]

Working on a change at https://dart-review.googlesource.com/c/sdk/+/240281/.

It will only work for server-provided snippets, which are currently something you can turn on if on Flutter master using the dart.enableServerSnippets setting but will automatically be enabled when your SDK supports them in an upcoming release of the VS Code extension.

[DanTup]

Landed in dart-lang/sdk@fa024be.

[eseidelGoogle]

Re: snippets, do https://github.com/Dart-Code/Dart-Code/blob/master/snippets/flutter.json also need to change?