RFR: 8294074: Make other specs more discoverable from the API docs

[Hannes Wallnöfer]

Please review a doc-only change to the API overview page to make other specs more discoverable. 

The new API overview page [can be viewed here](https://cr.openjdk.org/~hannesw/8294074/docs.00/api/index.html).

-------------

Commit messages:
 - JDK-8294074: Revert indentation changes
 - JDK-8294074: Make other specs more discoverable from the API docs

Changes: https://git.openjdk.org/jdk/pull/26547/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26547&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294074
  Stats: 6 lines in 1 file changed: 3 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/26547.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26547/head:pull/26547

PR: https://git.openjdk.org/jdk/pull/26547