Revert azure-pipelines-task-lib to 2.12.2 to mitigate shelljs bundling issue

[rbbarad]

Description

Background

This is a follow-up pr to fix the issue in #522.

Mark shelljs as external for esbuild bundling attempted to address this issue, but was not a successful solution for all of our tasks, as some of our tasks need the commands present in ShellJS.

Problem

This issue emerged with the bump of azure-pipelines-task-lib dependency in: #473.

Problem detailed in the open issue on azure-pipelines-task-lib repo: Cannot use JS bundler because of shelljs dependency.

Essentially, the toolkit takes a dependency on azure-pipelines-task-lib which takes an additional dependency on ShellJS. Our toolkit uses the esbuild JS Bundler to build the extension. This fails to bundle ShellJS because it uses dynamic require statements (problematic ShellJS code) instead of explicit require statements, which prevents bundlers from correctly analyzing the dependencies.

• In short, require('./a') works but require('./' + 'a') doesn't.

ShellJS has no plans to accommodate these explicit requires statements

Solution

Before making any larger scale changes, let's get azure-pipelines-task-lib back to its last known healthy state (working version we used for last release). This PR addresses that.

Future azure-pipelines-task-lib updates

Whenever we next bump the azure-pipelines-task-lib major version, we'll need to keep an eye on updates to microsoft/azure-pipelines-task-lib#942 for any new fixes or workarounds. Current known workarounds involve forking the ShellJS repository, making the necessary changes to ShellJS, and overriding the ShellJS dependency in package.json with the forked version.

• Example of forked ShellJS with hardcoded explicit requires statements
• Example of creating a bundler plugin with a fixed ShellJS file at compile time

Testing

• Ran unit tests
• ran tasks locally (using node <path-to-task>) to confirm output matches expectations
• Ran tasks/pipelines on hosted server and confirmed they run successfully

Checklist

• I have read the README document
• I have read the CONTRIBUTING document
• My code follows the code style of this project
• I have added tests to cover my changes
• A short description of the change has been added to the changelog using the script npm run newChange

License

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.