RFR: 8294074: Make other specs more discoverable from the API docs [v3]

[Hannes Wallnöfer]

> Please review a doc-only change to the API overview page to make other specs more discoverable. The following sentence is added at the end of the overview text:
> 
>> [Related documents](https://cr.openjdk.org/~hannesw/8294074/docs.00/specs/index.html) specify the Java language, the Java virtual machine, various protocols and file formats pertaining to the Java platform, and tools included in the JDK.
> 
> The first sentence of the overview text is also rephrased.
> 
> The new API overview page [can be viewed here](https://cr.openjdk.org/~hannesw/8294074/docs.00/api/index.html).

Hannes Wallnöfer has updated the pull request incrementally with one additional commit since the last revision:

  Minor changes

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26547/files
  - new: https://git.openjdk.org/jdk/pull/26547/files/7f038dea..e96c73da

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26547&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26547&range=01-02

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 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