Is your feature request related to a problem? Please describe.
With most code blocks contained in curly braces ({}), you are able to collapse/fold them. With an enum (that can take up multiple lines with trailing commas or otherwise), you are unable to fold these "blocks".

Describe the solution you'd like
I'd like to be able to fold an dart enum in VS Code.

enum LoremIpsum {
  dolor,
  sit,
  amet,
  consectetur,
  adipiscing,
  elit,
  sed,
  eiusmod,
  tempor,
  incididunt,
  ut,
  labore,
}

to

enum LoremIpsum {...
}

Describe alternatives you've considered
I've looked around at some settings, but I can't seem to find any obvious rules/settings to enable this behavior.

Additional context
In unsaved documents (Untitled-1-like) I am able to fold them with Dart language mode on. But once I save them as a .dart file, the option is gone. See images below.

Before saving file:

Can fold:

After saving file: