RFR: 8333768: Minor doc updates to java.lang.{Float, Double}

[Joe Darcy]

Misc small doc updates and addition of `@Overrides` annotations.

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Commit messages:
 - JDK-8333768: Minor doc updates to java.lang.{Float, Double}

Changes: https://git.openjdk.org/jdk/pull/19590/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19590&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333768
  Stats: 55 lines in 2 files changed: 40 ins; 2 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/19590.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19590/head:pull/19590

PR: https://git.openjdk.org/jdk/pull/19590