[match-case]: mapping pattern narrowing inconsistent with equivalent `isinstance` narrowing

[randolf-scholz]

Code sample in pyright playground

from typing import assert_type
from collections.abc import Mapping

def test_instance(x: dict | int) -> None:
    if isinstance(x, Mapping):
        assert_type(x, dict)  # ✅️
    else:
        assert_type(x, int)  # ✅️

def test_match(x: dict | int) -> None:
    match x:
        case {}:  # equivalent to isinstance(x, Mapping)
            assert_type(x, dict)  # ❌️
        case _:
            assert_type(x, int)  # ❌️

Additionally, there are some failures related to TypeDict with mapping patterns: Code sample in pyright playground