Various class based NamedTuple and TypedDict errors not caught

This example has a bunch of errors that the semantic analyzer should probably report (and one what seems like a false positive):

from typing import NamedTuple, TypeVar, Generic
from typing_extensions import Protocol
from mypy_extensions import TypedDict

@xyz  # No error
class N1(NamedTuple):
   x: int

@xyz  # No error
class T1(TypedDict):
    x: int

class N2(NamedTuple, Protocol):  # No error
   x: int

class T2(TypedDict, Protocol):  # No error
    x: int

class M(type):
    def f(cls) -> None: pass

class N3(NamedTuple, metaclass=M):  # No error
   x: int

N3.f()  # Error

class T3(TypedDict, metaclass=M):  # No error
    x: int

T = TypeVar('T')

class N4(NamedTuple, Generic[T]):  # No error
   x: int

class T4(TypedDict, Generic[T]):  # No error
   x: int

Start by reproducing the Python example and tracing the semantic analyzer handling of class-based NamedTuple and TypedDict definitions. Compare diagnostics for decorators, Protocol and metaclass bases, and Generic combinations with the expectations in the issue, including the reported false positive. Done means the missing errors are reported and the false positive is addressed.