feat: add CurrencyAmount.{greaterThan,equalTo,lessThan}

[olehmisar]

I am using sdk-core for my projects and safety checks on this.currency.equals(other.currency) for CurrencyAmount would be great. Something like this(you may want to omit | 0 but this is quite handy in practice)

class CurrencyAmount<T> {
  ...

  public greaterThan(other: CurrencyAmount<T> | 0): boolean {
    invariant(other === 0 || this.currency.equals(other.currency), "CURRENCY");
    return super.greaterThan(other);
  }
  
  public equalTo(other: CurrencyAmount<T> | 0): boolean {
    invariant(other === 0 || this.currency.equals(other.currency), "CURRENCY");
    return super.equalTo(other);
  }
  
  public lessThan(other: CurrencyAmount<T> | 0): boolean {
    invariant(other === 0 || this.currency.equals(other.currency), "CURRENCY");
    return super.lessThan(other);
  }
}