Implement Black's allow_empty_first_line_before_new_block_or_comment as a Ruff preview style.

def foo():
    """
    Docstring
    """

    # Here we go
    if x:

        # This is also now fine
        a = 123

    else:
        # But not necessary
        a = 123

Notice how black now allows empty lines before the comments. Ruff seems to support this sometimes.

Goal: Implement the new formatting behind the preview flag and import the Black tests.