RFR: 8343442: Add since checker tests to the networking area modules [v4]

[Nizar Benalla]

> Can I please get a review for this patch that brings the `@since` test described [here](https://mail.openjdk.org/pipermail/jdk-dev/2024-October/009474.html) to the networking area modules.
> 
> The benefit from this is helping API authors and reviewer validate the accuracy of `@since` in their source code (and subsequently, in the generated documentation).
> 
> The test has been added for `java.base` 2 weeks ago and has helped catch some bugs before they make it to the JDK.
> 
> Note: the `@modules` declarations are missing from the jtreg comment because we will now include them in a `TEST.properties` file.
> 
> TIA

Nizar Benalla has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:

 - Merge remote-tracking branch 'upstream/master' into since-checks-net-area
 - Rename tests and directories under modules dir
 - make jtreg comment more concise
 - This file should not have been changed
 - add a test for since tags in the source to the networking area modules

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Changes: https://git.openjdk.org/jdk/pull/21838/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21838&range=03
  Stats: 9 lines in 3 files changed: 0 ins; 0 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/21838.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21838/head:pull/21838

PR: https://git.openjdk.org/jdk/pull/21838