RFR: 8368349: Add library notes discussing abs and IEEE 754 operations

[Joe Darcy]

Add apiNote linking {Math, StrictMath}.abs to the IEEE 754 abs operation.

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Commit messages:
 - JDK-8368349: Add library notes discussing abs and IEEE 754 operations

Changes: https://git.openjdk.org/jdk/pull/27443/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27443&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8368349
  Stats: 16 lines in 2 files changed: 16 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27443.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27443/head:pull/27443

PR: https://git.openjdk.org/jdk/pull/27443