RFR: [type-classes] JDK-8376823: Add prototype polynomial class

[Joe Darcy]

Add a simple polynomial class over doubles as an example of a ring.

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Commit messages:
 - Appease jcheck.
 - JDK-8376823: Add prototype polynomial class

Changes: https://git.openjdk.org/valhalla/pull/2004/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=2004&range=00
  Stats: 464 lines in 1 file changed: 464 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/valhalla/pull/2004.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/2004/head:pull/2004

PR: https://git.openjdk.org/valhalla/pull/2004