RFR: 8378414: Add methods to test for representation equivalence [v2]

[Joe Darcy]

> Floating-point values have a notion of representation equivalence distinct from the comparison done by ==. This notion of equivalence could have a method to provide the predicate directly, rather than relying on one of several expressions listed in the documentation ([JDK-8295391](https://bugs.openjdk.org/browse/JDK-8295391)).

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

  Respond to review feedback; add build tags.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/29870/files
  - new: https://git.openjdk.org/jdk/pull/29870/files/8f630ca0..f843a832

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=29870&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=29870&range=00-01

  Stats: 8 lines in 4 files changed: 4 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/29870.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29870/head:pull/29870

PR: https://git.openjdk.org/jdk/pull/29870