[ty] Fix narrowing and reachability of class patterns with arguments

[sharkdp]

Summary

I noticed that our type narrowing and reachability analysis was incorrect for class patterns that are not irrefutable. The test cases below compare the old and the new behavior:

from dataclasses import dataclass

@dataclass
class Point:
    x: int
    y: int

class Other: ...

def _(target: Point):
    y = 1

    match target:
        case Point(0, 0):
            y = 2
        case Point(x=0, y=1):
            y = 3
        case Point(x=1, y=0):
            y = 4
    
    reveal_type(y)  # revealed: Literal[1, 2, 3, 4]    (previously: Literal[2])


def _(target: Point | Other):
    match target:
        case Point(0, 0):
            reveal_type(target)  # revealed: Point
        case Point(x=0, y=1):
            reveal_type(target)  # revealed: Point    (previously: Never)
        case Point(x=1, y=0):
            reveal_type(target)  # revealed: Point    (previously: Never)
        case Other():
            reveal_type(target)  # revealed: Other    (previously: Other & ~Point)

Test Plan

New Markdown test

[github-actions]

mypy_primer results

No ecosystem changes detected ✅
No memory usage changes detected ✅

[carljm]

Thank you!