Provide methods for checking if an object is `FileHandle` (`node:fs`)

[JustappleJust]

What is the problem this feature will solve?

Sometimes, package developers want to allow users to specify a file path, fd (a number), or FileHandle as a single parameter for file operations. Unfortunately, there isn’t a reliable method for developers to check if an instance of the FileHandle class is provided. By implementing this feature, developers can easily and consistently check for the presence of a FileHandle instance.

What is the feature you are proposing to solve the problem?

I propose adding the following methods to the support:

1. Make the FileHandle class accessible from fs.FileHandle or fs.promises.FileHandle, allowing developers to check directly with instanceof.
2. Implement a static method FileHandle.isFileHandle(), similar to what Buffer does.
3. If feasible, provide a method in FileHandle(fd) or FileHandle.from(fd) to convert a fd number into a FileHandle.

What alternatives have you considered?

Checking the object’s methods and properties directly is not a smart approach. Obtaining the FileHandle class by opening any file is slow.

[amyssnippet]

great observation @JustappleJust i have tried to reproduce the issue and i thnk the feature should be there

I would like to work on exposing FileHandle in node:fs/promises and node:fs to solve this.

Complete Details of Reproduction of Issue

amol@Amols-MBP Desktop % cat test.js 
const fs = require('node:fs');
const fsPromises = require('node:fs/promises');

async function test() {
  // 1. Check if the class is exported on the main module
  console.log('fs.FileHandle:', fs.FileHandle); // Expect: undefined
  console.log('fsPromises.FileHandle:', fsPromises.FileHandle); // Expect: undefined

  // 2. Get a real FileHandle instance to test against
  const handle = await fsPromises.open(__filename, 'r');
  
  try {
    // 3. Try to use instanceof (This is what the user WANTS to do)
    // This will throw ReferenceError because FileHandle isn't a global or exported
    try {
      console.log('Is instance of fs.FileHandle?', handle instanceof fs.FileHandle);
    } catch (e) {
      console.log('Cannot check instanceof fs.FileHandle:', e.message);
    }

    // 4. The current "ugly" workaround (Duck Typing)
    const isFileHandle = typeof handle === 'object' && 
                         handle !== null && 
                         typeof handle.fd === 'number' &&
                         typeof handle.close === 'function';
    
    console.log('Current ugly check result:', isFileHandle);

  } finally {
    await handle.close();
  }
}

test();
amol@Amols-MBP Desktop % node -v
v24.13.0
amol@Amols-MBP Desktop % node test.js 
fs.FileHandle: undefined
fsPromises.FileHandle: undefined
Cannot check instanceof fs.FileHandle: Right-hand side of 'instanceof' is not an object
Current ugly check result: true
amol@Amols-MBP Desktop %