RFR: 8317621: --add-script should support JavaScript modules [v2]

[Hannes Wallnöfer]

> Please review an enhancement to detect [JavaScript modules](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules) when added to `javadoc` with the `--add-script` option, which require a different `type` attribute in the HTML `<script>` element. The main method of detection is to scan the script content for `import` and `export` statements. The `*.mjs` extension is also recognized, although it is rarely used for browser modules. 
> 
> I have tested the recognition against scripts and modules in projects such as [Angular](https://github.com/angular/angular) and [Mermaid](https://github.com/mermaid-js/mermaid) and it worked quite well in detecting JavaScript modules.

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

  Address review feedback

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18546/files
  - new: https://git.openjdk.org/jdk/pull/18546/files/3c7043de..5a79ded2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18546&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18546&range=00-01

  Stats: 39 lines in 1 file changed: 20 ins; 16 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/18546.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18546/head:pull/18546

PR: https://git.openjdk.org/jdk/pull/18546