Add an option to disable auto-formatting of the action "Fill struct fields"

Hi.
Since a couple of weeks, the action "Fill struct fields" will automatically format the code.
This often results in putting all the fields on the same line which I find harder to edit compared to the previous behavior of having one of them per line.
And usually, after adding the values, it will be formatted on multiple lines anyway, so I don't see much benefit to auto-format the result of this action immediately.

For this code:

                            args: vec![TypedExpr {
                            }],

rust-analyzer would previous give the following code after the action:

                            args: vec![TypedExpr {
                                expr: todo!(),
                                pos,
                                typ: todo!(),
                            }],

now it gives:

                            args: vec![TypedExpr { expr: todo!(), pos, typ: todo!() }],

Could you please add a setting to disable the auto-formatting (so that we get the previous behavior) for actions like this?
Thanks.

Start by locating the implementation of the "Fill struct fields" action and where it invokes formatting. Trace how action settings are represented, then determine how an option could preserve the previous multiline output. Done means the action can skip auto-formatting when the option is disabled, while retaining current behavior by default and covering both modes with tests.