gn format: properly break and align multiple suffix comments

Previously

  a = [
    "x",
    "y",   # Comment1
           # Comment2
  ]

would turn into
  a = [
    "x",
    "y",   # Comment1# Comment2
  ]

(Child of https://codereview.chromium.org/606123002/)

[email protected]
BUG=348474

Review URL: https://codereview.chromium.org/613473002

Cr-Commit-Position: refs/heads/master@{#297235}
4 files changed