[Flpvoigt]

Summary

Pyrefly previously did not provide completion suggestions for attributes dynamically handled by __getattr__.

This change reads the string literals from the parameter after self. For example, when the parameter is annotated with Literal["A", "B"], Pyrefly suggests A and B as attribute completions while avoiding duplicates with attributes already defined on the class.

Fixes #5312

Original description in Portuguese

Foi implementado o autocomplete de atributos definidos dinamicamente pelo __getattr__.

Antes, neste código:

from typing import Literal

class A:
    def __getattr__(self, item: Literal["A", "B"]) -> object: ...

A().

o Pyrefly não sugeria nada relacionado ao Literal.

Agora ele:

- encontra o método __getattr__;
- identifica o parâmetro depois de self;
- lê os valores de Literal["A", "B"];
- oferece A e B no autocomplete;
- evita repetir nomes que já sejam atributos reais da classe.
</details>

- [ ] I am a human, and I fully understand the code I am submitting.

# Test Plan

- Added a language server completion test for Literal["A", "B"].
- Ran cargo test -p pyrefly --lib dot_complete_from_getattr_literal_parameter --jobs 1.
- Result: 1 passed; 0 failed.

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[rchen152]

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