Consider `__getattr__` in structural subtyping

[yangdanny97]

Describe the Bug

Right now we raise an error if an attribute is available only through __getattr__. I also don't like that the error message says P.x "or" C.x when we know exactly which one it is.

I think this is a TODO:

pyrefly/pyrefly/lib/alt/attr.rs

Line 1456 in ce5d522

// NOTE(grievejia): `__getattr__` does not participate in structural subtyping

from typing import *

class P(Protocol):
    x: int

class C:
    def __getattr__(self, attr) -> int:
        return 1

p: P = C()

Sandbox Link

https://pyrefly.org/sandbox/?project=N4IgZglgNgpgziAXKOBDAdgEwEYHsAeAdAA4CeS4ATrgLYAEALqcROgOZ0Q3G6UN0AqADroRAYyio4cOgAUAFLOoNcY3FACUiEXV118iTugYjxk6XQDC29HrqYYYOgH1nbGA1QMGlV-LgwUGAANHRePhp0ALQAfEYMNnZ2lB4ArpS2AIym6MSGsnQAvFbyGiDBIGQpYFCkhCo0UBQAxHKk1bV0aFh4%2BHRq6JBs6V4QuOiEIq0AyjAwdAAW3sRwiAD0a1WOtYS8bGsw6GuYqnBrA0MjDGNHdGC8YQBuqNCo2LD945eUo%2BN0uMRruM4JNcqQGAtxlFHjBKHAbkU6EIQABmQiZABMyJEAG1YdQ4QBdESpdBcHh8GCYKKYCApMTXGGIgDkEDY6F4MGZIg5DCiKQAjqk6VSogBrGCkKKoMRieAyYrMgDuqAy3PQIAAvhUZYyYAAxaAwCjdHAEEjkTVAA

(Only applicable for extension issues) IDE Information

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