Consider extending proposal to all class element definitions

[pzuraq]

Following this thread, I think this proposal could be generalized to allow defining any type of class element in the class element block, not just accessors. This would add the ability set properties like writable and enumerable on class elements, and could also potentially be a reason to reconsider whether or not a syntactic opt-in is required (since this would be a much more general syntax than just auto accessors):

class C {
  identifier {
    writable?: boolean;
    enumerable?: boolean;
    configurable?: boolean;

    value?: unknown;
    get?: () => T;
    set?: (v: T) => void;
  }: T;
}

We could also have a much shorter opt-in keyword, define or def, instead of accessor:

class C {
  // `define` keyword
  define x { writable = false } = 123;
  @reactive define x { get; set; } = 123;

  // `def` keyword
  def x { writable = false } = 123;
  @reactive def x { get; set; } = 123;
}

I did a quick write-up of what this could potentially look like, it overlaps a lot with this proposal: https://gist.github.com/pzuraq/ae002a0f3e8745b57cd6c046bf9ff89f

[rbuckton]

I'm not comfortable with reifying property descriptors as an independent class element. If we want to give someone a way to modify other descriptor properties such as enumerability, I think we're better off introducing specific keywords or some kind of native decorator that has privileged access to the descriptor internally.