Private slot declarations need to be in constructor scope

[erights]

tc39/proposal-class-public-fields#2 and tc39/proposal-private-fields#25 apply here as well. Notice the existing notational redundancy in examples such as

class {
  private #data1;
  constructor(d) {
    #data1 = d; 
  }
}

If this is written instead as

class {
  constructor(d) {
    private #data1 = d; 
  }
}

then this line would be all that is necessary to declare and initialize this private slot in a data-dependent way. As with tc39/proposal-class-public-fields#2 and tc39/proposal-private-fields#25 , this would smoothly accommodate future support for const private slots, which must be initialized and cannot be assigned.

[erights]

Closing for the same reasons that closed tc39/proposal-private-fields#25 and tc39/proposal-class-public-fields#2