No Fix-It for @main struct without main static function

[ahoppen]

When compiling the following code, you get an error message: 'Foo' is annotated with @main and must provide a main static function of type () -> Void, () throws -> Void, () async -> Void, or () async throws -> Void

@main struct Foo {
}

We should offer a fix-it to add

static func main() {
  <#code#>
}

I’m open to whether we should also suggest the async and throws variations but IMHO just offering the base variation without any modifiers would be a good starting point.

rdar://92511524