Improve "outdated trace" error message

- Refactor WinscopeError machinery to support more flexible messages
- Replace the ambiguous error message
  "<filename>: discarded because outdated"
  with a clearer
  "<filename>: discarded because data is older than <time>"

Fix: 318826684
Test: npm run test:presubmit
Change-Id: Iea8324aa927a26587d1872b617e2acd1833f8e38
10 files changed