Fix type narrowing bug

[gramster]

Fix isMaybeDescriptorInstance to use MRO lookup for inherited descriptors

Updated isMaybeDescriptorInstance to use lookUpObjectMember for MRO-aware lookup of get and set methods, fixing all ~6 call sites that were broken for descriptor subclasses. Simplified typeGuards.ts to use the fixed utility function instead of custom MRO lookup logic.

Fixes #11039

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

sympy (https://github.com/sympy/sympy)
-   .../projects/sympy/sympy/solvers/diophantine/diophantine.py:176:44 - error: Cannot access attribute "expand" for class "Basic"
-     Attribute "expand" is unknown (reportAttributeAccessIssue)
-   .../projects/sympy/sympy/solvers/diophantine/tests/test_diophantine.py:314:30 - error: Cannot access attribute "as_independent" for class "Basic"
-     Attribute "as_independent" is unknown (reportAttributeAccessIssue)
-   .../projects/sympy/sympy/solvers/diophantine/tests/test_diophantine.py:383:30 - error: Cannot access attribute "as_independent" for class "Basic"
-     Attribute "as_independent" is unknown (reportAttributeAccessIssue)
+   .../projects/sympy/sympy/solvers/ode/single.py:867:9 - error: Expression with type "tuple[ComplexInfinity | NaN | Rational | Zero | Infinity | NegativeInfinity | Float | NotImplementedType | Expr | Unknown | Any, list[tuple[Unknown, Unknown]] | list[Unknown]] | tuple[ComplexInfinity | NaN | Rational | Zero | Infinity | NegativeInfinity | Float | NotImplementedType | Expr | Unknown | Any, list[tuple[Unknown, Unknown]] | list[Unknown], list[tuple[Unknown, Unknown]] | list[Unknown]]" cannot be assigned to target tuple
+     Type "tuple[ComplexInfinity | NaN | Rational | Zero | Infinity | NegativeInfinity | Float | NotImplementedType | Expr | Unknown | Any, list[tuple[Unknown, Unknown]] | list[Unknown], list[tuple[Unknown, Unknown]] | list[Unknown]]" is incompatible with target tuple
+       Tuple size mismatch; expected 2 but received 3 (reportAssignmentType)
-   .../projects/sympy/sympy/solvers/ode/systems.py:1214:26 - error: Argument of type "dict[str, str | Unknown | Pow | bool | Symbol]" cannot be assigned to parameter "m" of type "Iterable[tuple[str, str]]" in function "update"
+   .../projects/sympy/sympy/solvers/ode/systems.py:1214:26 - error: Argument of type "dict[str, str | Unknown | Expr | bool | Symbol]" cannot be assigned to parameter "m" of type "Iterable[tuple[str, str]]" in function "update"
-   .../projects/sympy/sympy/vector/implicitregion.py:188:18 - error: Operator "/" not supported for types "int | Unknown" and "Alg | Unknown | GaussianRational | MPQ | GaussianInteger | MPZ | Expr | Rational | NaN | ComplexInfinity | One | NegativeOne | Zero | Integer | Infinity | NegativeInfinity | Float | Number | Poly | Any"
-     Operator "/" not supported for types "int" and "MPZ" (reportOperatorIssue)
-   .../projects/sympy/sympy/vector/implicitregion.py:189:18 - error: Operator "/" not supported for types "int | Unknown" and "Alg | Unknown | GaussianRational | MPQ | GaussianInteger | MPZ | Expr | Rational | NaN | ComplexInfinity | One | NegativeOne | Zero | Integer | Infinity | NegativeInfinity | Float | Number | Poly | Any"
-     Operator "/" not supported for types "int" and "MPZ" (reportOperatorIssue)
-   .../projects/sympy/sympy/vector/implicitregion.py:190:18 - error: Operator "/" not supported for types "int | Unknown" and "Alg | Unknown | GaussianRational | MPQ | GaussianInteger | MPZ | Expr | Rational | NaN | ComplexInfinity | One | NegativeOne | Zero | Integer | Infinity | NegativeInfinity | Float | Number | Poly | Any"
-     Operator "/" not supported for types "int" and "MPZ" (reportOperatorIssue)
-   .../projects/sympy/sympy/vector/implicitregion.py:206:18 - error: Operator "*" not supported for types "Unknown | Expr | Any" and "Alg | Unknown | GaussianRational | MPQ | GaussianInteger | MPZ | Expr | Rational | NaN | ComplexInfinity | One | NegativeOne | Zero | Integer | Infinity | NegativeInfinity | Float | Number | Poly | Any"
-     Operator "*" not supported for types "Expr" and "GaussianRational"
-     Operator "*" not supported for types "Expr" and "MPQ"
-     Operator "*" not supported for types "Expr" and "GaussianInteger"
-     Operator "*" not supported for types "Expr" and "MPZ" (reportOperatorIssue)
-   .../projects/sympy/sympy/vector/implicitregion.py:210:18 - error: Operator "*" not supported for types "Unknown | Expr | Any" and "Alg | Unknown | GaussianRational | MPQ | GaussianInteger | MPZ | Expr | Rational | NaN | ComplexInfinity | One | NegativeOne | Zero | Integer | Infinity | NegativeInfinity | Float | Number | Poly | Any"
-     Operator "*" not supported for types "Expr" and "GaussianRational"
-     Operator "*" not supported for types "Expr" and "MPQ"
-     Operator "*" not supported for types "Expr" and "GaussianInteger"
-     Operator "*" not supported for types "Expr" and "MPZ" (reportOperatorIssue)
-   .../projects/sympy/sympy/vector/implicitregion.py:214:18 - error: Operator "*" not supported for types "Unknown | Expr | Any" and "Alg | Unknown | GaussianRational | MPQ | GaussianInteger | MPZ | Expr | Rational | NaN | ComplexInfinity | One | NegativeOne | Zero | Integer | Infinity | NegativeInfinity | Float | Number | Poly | Any"
-     Operator "*" not supported for types "Expr" and "GaussianRational"
-     Operator "*" not supported for types "Expr" and "MPQ"
-     Operator "*" not supported for types "Expr" and "GaussianInteger"
-     Operator "*" not supported for types "Expr" and "MPZ" (reportOperatorIssue)
- 38415 errors, 84 warnings, 0 informations
+ 38407 errors, 84 warnings, 0 informations