RFR: 8341100: Add index entries for terms used in java.lang.Class

[Joe Darcy]

Small update to java.lang.Class docs.

I didn't add an index item for "hidden classes" since the indexing mechanism picks up the section titles.

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Commit messages:
 - Refine changes.
 - Merge branch 'master' into JDK-8341100
 - JDK-8341100: Add index entries for terms used in java.lang.Class

Changes: https://git.openjdk.org/jdk/pull/21241/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21241&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341100
  Stats: 9 lines in 1 file changed: 2 ins; 1 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/21241.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21241/head:pull/21241

PR: https://git.openjdk.org/jdk/pull/21241