Running `get_dynamic_class_hook()` after `get_class_decorator_hook_2()`

Feature

It would be useful to run get_dynamic_class_hook() from plugins after get_class_decorator_hook_2() to support dynamic classes that inspect existing dataclasses / attrs classes.

Pitch

We have an internal mypy plugin that makes "partial" classes, where all required attributes are optional. It does this by examining the __init__ of an attrs class and creating a new __init__ for the new class where all args are now optional. This works in mypy 0.942, occasionally crashes in 0.950, and doesn't work at all in 0.960 (128661ccbf4396ed1538421c481f1773c7490169) because the attrs __init__ is not present during get_dynamic_class_hook().

Is there some way to work around this?

Inizia tracciando i punti di ingresso del plugin get_dynamic_class_hook() e get_class_decorator_hook_2() e il modo in cui l'ordine degli hook espone i metodi init generati da attrs. La modifica è completa quando gli hook delle classi dinamiche possono ispezionare dataclasses o classi attrs esistenti dopo l'elaborazione dei decoratori, con copertura di regressione per lo scenario del plugin partial-class descritto qui.