neovim: `gq` inside Python docstrings

[dwf]

I'd prefer a fallback to the built-in behaviour when formatting text that falls fully inside a docstring.

A Treesitter expression for this seems to be

(body: block
  (expression_statement
    (string)))

i.e. a string appearing as an expression_statement node appearing directly inside a body's block.

Might want to only use the string_content inside.