Fix type inference for class-level @property access (#3958)

[AMR5210]

Summary

When accessing a @property decorated method directly on a class (e.g., Foo.bar), the type checker previously incorrectly inferred the return type of the getter function. This PR updates pyrefly/lib/alt/expr.rs to correctly return the property descriptor object itself via self.stdlib.property() when the base type is a ClassDef and the attribute has property_metadata.

Fixes #3958

Test Plan

Verified locally in strict mode using reveal_type() on class-level property access to ensure the descriptor type is returned rather than the getter's return type.

Test code (test_property.py):

class Foo:
    @property
    def bar(self) -> int:
        return 42

reveal_type(Foo.bar)

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