Preserve blank line before raw docstrings

[konstin]

Describe the style change

Currently, black preserves the blank line before regular doc strings, but not before raw docstrings. It should preserve them before both.

Input

class TextIOWrapper(TextIOBase):
    
    r"""Character and line based layer over a BufferedIOBase object, buffer.

    [...]
    """

    _CHUNK_SIZE = 2048
    
class TextIOWrapper(TextIOBase):
    
    """Character and line based layer over a BufferedIOBase object, buffer.

    [...]
    """

    _CHUNK_SIZE = 2048

Examples in the current Black style

class TextIOWrapper(TextIOBase):
    r"""Character and line based layer over a BufferedIOBase object, buffer.

    [...]
    """

    _CHUNK_SIZE = 2048


class TextIOWrapper(TextIOBase):

    """Character and line based layer over a BufferedIOBase object, buffer.

    [...]
    """

    _CHUNK_SIZE = 2048

Desired style

class TextIOWrapper(TextIOBase):

    r"""Character and line based layer over a BufferedIOBase object, buffer.

    [...]
    """

    _CHUNK_SIZE = 2048


class TextIOWrapper(TextIOBase):

    """Character and line based layer over a BufferedIOBase object, buffer.

    [...]
    """

    _CHUNK_SIZE = 2048

Additional context

Currently, black doesn't seem to consider raw triple quotes strings as docstrings, even though cpython (and PEP 257) do. I've seen some raw triple quoted doc string uses in the wild, such as the above example from cpython.

[JelleZijlstra]

We should actually remove both blank lines: we do that in #3692 (currently only in the preview style). Agree that we should treat raw strings like docstrings too.