Formatter: Detect ObjC message expressions after 'in' in loop

Before:
  for (id foo in[self getStuffFor : bla]) {
  }

Now:
  for (id foo in [self getStuffFor:bla]) {
  }

"in" is treated as loop keyword if the line starts with "for", and as a
regular identifier else. To check for "in", its IdentifierInfo is handed
through a few layers.