JS: Add support for async readFile

[Napalys]

This pull request aims to resolve reported issue related to require("fs").promises.readFile() showing no data node found.

[Copilot]

Pull Request Overview

This pull request adds support for asynchronous file reading via fs.promises.readFile in our JavaScript security query tests to address the reported issue with missing data nodes. Key changes include:

• In the test file, an async IIFE is added to read the ".npmrc" file and use its content in an HTTP request.
• A new markdown change note is added documenting support for async file reads.

Reviewed Changes

Copilot reviewed 2 out of 4 changed files in this pull request and generated no comments.

File	Description
javascript/ql/test/query-tests/Security/CWE-200/FileAccessToHttp.js	Added an async function to read file data and incorporate it in an HTTP request for security analysis.
javascript/ql/lib/change-notes/2025-03-26-async-fileRead.md	Added a change note summarizing the support for async file reads.

Files not reviewed (2)

• javascript/ql/lib/semmle/javascript/frameworks/NodeJSLib.qll: Language not supported
• javascript/ql/test/query-tests/Security/CWE-200/FileAccessToHttp.expected: Language not supported

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[erik-krogh]

What was the motivation for this PR?
With a change like this I had maybe expected a backref to an internal issue? (So a link inside the internal issue to this PR).

My first thought was that this could be done nicer with Promises::valueProp() and a dataflow step.
But looking closer at how getADataNode() is used (directly as a source), I don't think that's an easier (or nicer) solution.

So this solution looks a bit crude to my eyes, but I think it's fine.

The change-note needs to change though.