`dataclasses` plugins does not respect `slots=True` argument

[sobolevn]

Since 3.10 now has slots=True argument for @dataclass decorator, we need to support it, since #10864 is merged.

Failing case right now:

from dataclasses import dataclass

@dataclass(slots=True)
class Some:
    x: int

    def __init__(self, x: int) -> None:
        self.x = x  # ok
        self.y = 1  # should be an error, but `mypy` is ok
        # Traceback (most recent call last):
        #   ...
        # AttributeError: 'Some' object has no attribute 'y'

Compare it with regular class, which works fine:

class Some:
    __slots__ = ('x',)

    def __init__(self, x: int) -> None:
        self.x = x  # ok
        self.y = 1  # E: Trying to assign name "y" that is not in "__slots__" of type "ex.Some"

Docs: https://docs.python.org/3/library/dataclasses.html#dataclasses.dataclass

Refs #11463

[sobolevn]

I cannot assign myself, but consider me assigned 🙂

[sobolevn]

We also need to check for slots confict:

from dataclasses import dataclass

@dataclass(slots=True)
class Some:
    __slots__ = ('x',)
    x: int
# Traceback (most recent call last):
#   ...
# TypeError: Some already specifies __slots__