fix up indentation in formatting guide

[cartermp]

This was mistakenly suggesting something that won't work. This now uses the formatting that we do in the F# compiler for our own very very long member definitions (sometimes). Fixes #18637

[knocte]

I feel like the ReturnType is too much on the right here:

    member _.LongMethodWithLotsOfParameters(aVeryLongType: AVeryLongTypeThatYouNeedToUse,
                                            aSecondVeryLongType: AVeryLongTypeThatYouNeedToUse,
                                            aThirdVeryLongType: AVeryLongTypeThatYouNeedToUse): ReturnType =

Shouldn't we split that on to a new line like this?:

    member _.LongMethodWithLotsOfParameters(aVeryLongType: AVeryLongTypeThatYouNeedToUse,
                                            aSecondVeryLongType: AVeryLongTypeThatYouNeedToUse,
                                            aThirdVeryLongType: AVeryLongTypeThatYouNeedToUse)
                                                : ReturnType =

[cartermp]

Sure, seems reasonable

[cartermp]

@gewarren @IEvangelist can we get this one merged?

[gewarren]

One spelling mistake to fix and suggest adding a comma too.

[IEvangelist]

Looks good to me, we'll - thank you 🙏