Allow users and/or packages to create custom versions of "Wrap with ..." actions

[DanTup]

It doesn't seem like there's an issue specifically for this, but there has been some discussion across various other issues (and PRs like https://github.com/Dart-Code/Dart-Code/pull/4232).

There is a desire to have more options in the "Wrap with..." actions list. Sometimes package-specific widgets, and sometimes widgets that users feel they use a lot. Including all of them in the default list could make it unwieldy (and doesn't handle packages). Perhaps analysis server plugins are the best way to handle this, but they might also be a bit complex for simple uses where a user just wants a simple extra wrap for a widget.