Remove the setInputFiles os.read support

[ankur22]

What?

Removing the support for setInputFiles to read off of the filesystem with the os package.

Why?

We do not want k6 to be able to read anything off of a filesystem that it shouldn't be reading. Instead anyone wishing to work with files on the filesystem should look to use the built in experimental fs module. The fs module abstracts away the detail of how it loads the required file for when working in a remote environment. It also reduces the risk of OOMs. A simple example can be found below:

Example working with `setInputFiles` and the fs module

import { browser } from 'k6/experimental/browser';
import encoding from 'k6/encoding';
import { open } from 'k6/experimental/fs';

export const options = {
  scenarios: {
    ui: {
      executor: 'shared-iterations',
      iterations: 1,
      vus: 1,
      options: {
        browser: {
          type: 'chromium'
        },
      },
    },
  },
}

let file;
(async function () {
  file = await open('/abs/path/to/file.txt');
})();

export default async function () {
  const page = browser.newPage();

  await page.goto(url)

  const buffer = await readAll(file);

  page.setInputFiles('input[id="upload"]', { name: 'file.txt', mimetype: 'text/plain', buffer: encoding.b64encode(buffer) })
  
  const submitButton = page.locator('input[type="submit"]')
  await Promise.all([page.waitForNavigation(), submitButton.click()])

  page.close();
}

async function readAll(file) {
  const fileInfo = await file.stat();
  const buffer = new Uint8Array(fileInfo.size);

  const bytesRead = await file.read(buffer);
  if (bytesRead !== fileInfo.size) {
    throw new Error(
      'unexpected number of bytes read; expected ' +
      fileInfo.size +
      ' but got ' +
      bytesRead +
      ' bytes'
    );
  }

  return buffer;
}

Checklist

• I have performed a self-review of my code
• I have added tests for my changes
• I have commented on my code, particularly in hard-to-understand areas

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