Preserve column-sensitive block layouts

[dearlordylord]

Preserve declarations containing inline case rows or unsupported do layouts while formatting neighbours. Only single-line do NAME<NAME>: headers with the first statement on the next line are formatted.

Old formatter output (fails to parse):

import Base
def main() -> IO(Unit):
  do IO<Unit>: IO.print("a")
    IO.print("b")

def other() -> U32:
  0

Fixed formatter output:

import Base
def main() -> IO(Unit):
  do IO<Unit>: IO.print("a")
               IO.print("b")

def other() -> U32:
  0