RFR: 8347605: Use spec tag to refer to IEEE 754 standard

[Joe Darcy]

Redo the work done in JDK-8285977 to use the `@spec` tag so that the IEEE floating-point standard gets listed as one of the external specifications.

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Commit messages:
 - JDK-8347605: Use spec tag to refer to IEEE 754 standard

Changes: https://git.openjdk.org/jdk/pull/23082/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23082&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8347605
  Stats: 30 lines in 7 files changed: 0 ins; 0 del; 30 mod
  Patch: https://git.openjdk.org/jdk/pull/23082.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23082/head:pull/23082

PR: https://git.openjdk.org/jdk/pull/23082