[ravenwood dashboard] @RavenwoodSupported is not boring

- If a public method has @RavenwoodSupported, make sure it shows up
  on the dashboard by not marking it as "boring".
  (even if it's abstract)

- Also clean up ravenwood-stats-collector.sh

- Add "csv-flattener" for "flattening" CSV -- this will print each
  column in a separate line, for a better diff result.

- Add "-d DIFF_BASE" option to ravenwood-stats-collector.sh to
  print diff against another CSV file.

Test: Manual test with comparing against the old CSV
Flag: EXEMPT script change only
Bug: 414821464

Change-Id: I1837222df6ae775e5804cd0d850891c76c0f5ed7