Spec change: float/int promotion is implemented through implicit unions

[JelleZijlstra]

I'd like to submit the spec change in https://github.com/python/typing/pull/1748, which clarifies that the float/int (and complex/float) implicit promotion is implemented by treating float as if it was float | int in type expressions. Discussion in https://discuss.python.org/t/clarifying-the-float-int-complex-special-case/54018/30 (and more related discussion in https://discuss.python.org/t/options-for-a-long-term-fix-of-the-special-case-for-float-int-complex/54289).

• [x] Carl
• [x] Eric
• [x] Jelle
• [ ] Jukka
• [x] Rebecca