RFR: Switch to GitHub's new review comment positioning API

[Robin Westberg]

Hi all,

Please review this change that switches to GitHub's new review comment positioning API. This removes the need for calculating line numbers based on position in the textual diff. Note that support for multi-line comments is not yet done (such comments will be shown as positioned on the last line). We can probably wait a bit with implementing that, as the API is technically still in preview.

Best regards,
Robin

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Commits:
 - 1c1ccd13: Switch to GitHub's new review comment positioning API

Changes: https://git.openjdk.java.net/skara/pull/269/files
 Webrev: https://webrevs.openjdk.java.net/skara/269/webrev.00
  Stats: 491 lines in 5 files changed: 30 ins; 424 del; 37 mod
  Patch: https://git.openjdk.java.net/skara/pull/269.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/269/head:pull/269

PR: https://git.openjdk.java.net/skara/pull/269