RFR: 8338529: Initial iteration of numerics modeling interfaces

[Joe Darcy]

A refinement of some earlier ideas on the numerics modeling interfaces to inform further discussions.

This is a "lumpy" rather than "splitty" design in terms of favoring a smaller number of interfaces with more functionality rather than a larger number of interfaces making smaller distinctions.

Various design comments and to-do's noted in the code.

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Commit messages:
 - Appease jcheck some more.
 - Appease jcheck
 - 8338529: Initial iteration of numerics modeling interfaces

Changes: https://git.openjdk.org/valhalla/pull/1917/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1917&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338529
  Stats: 592 lines in 4 files changed: 592 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/valhalla/pull/1917.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1917/head:pull/1917

PR: https://git.openjdk.org/valhalla/pull/1917