RFR: [type-classes] JDK-8376823: Add prototype polynomial class [v4]

[Joe Darcy]

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

Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:

  Misc refactorings.

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Changes:
  - all: https://git.openjdk.org/valhalla/pull/2004/files
  - new: https://git.openjdk.org/valhalla/pull/2004/files/e79bfa50..e4172202

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=2004&range=03
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=2004&range=02-03

  Stats: 13 lines in 1 file changed: 5 ins; 4 del; 4 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