Formatting issue with postfix if configs on `main`

[DavidBrunow]

I recently worked on #383 but noticed some behavior that I think is incorrect with the fix.

Given this code:

  EmptyView()
    .padding([.vertical])
  #if os(iOS)
    .iOSSpecificModifier()
  #endif  

The formatter incorrectly does not indent the .padding([.vertical]) on line 2:

Output:

  EmptyView()
  .padding([.vertical])
  #if os(iOS)
    .iOSSpecificModifier()
  #endif  

I have a potential fix and will put up a pull request soon.

[ahoppen]

Tracked in Apple’s issue tracker as rdar://126948251