Need a way to specify codegen behavior for enum items

[upsuper]

In nsCSSPropertyID enum, we have something like:

enum nsCSSPropertyID {
  eCSSProperty_a,
  eCSSProperty_b,
  // ...

  eCSSProperty_COUNT,
  eCSSProperty_COUNT_DUMMY2 = eCSSProperty_COUNT - 1,

  eCSSPropertyAlias_aa,
  eCSSPropertyAlias_bb,
  // ...
}

In this case, since eCSSPropertyAlias_aa would be identical to eCSSProperty_COUNT, it would become a separate constant rather than an enum item. This is undesired. Ideally, eCSSProperty_COUNT should become a constant, while eCSSPropertyAlias_aa should be an enum item.

I guess we can add something like

/// <div rustbindgen constant></div>

to bindgen to correct this kind of cases.

[emilio]

Fixed by #393 :)