Formatter: multiline_string_handling preview style

[MichaReiser]

Implement Black's multiline_string_handling as a preview style.

Ruff already implements (as part of stable) the new style when calling functions on a multiline string:

MULTILINE = """
foobar
""".replace(
    "\n", ""
)

Get's formatted to

MULTILINE = """
foobar
""".replace("\n", "")

However, Ruff doesn't yet implement the new style when passing a multiline string in a function call:

textwrap.dedent(
    """\
    This is a
    multiline string
"""
)

Gets formatted to:

textwrap.dedent("""\
    This is a
    multiline string
""")

Note: It's not yet decided if this style will make it into Black's 2024 stable style