Test: assist user in setting up eslint

[chrmarti]

See ESLint extension (see https://github.com/Microsoft/vscode-eslint)

• any OS - @octref

Complexity: 2

Setup:

• Install eslint-extension@latest
• create a new workspace and change dir into it
• npm install eslint
• open workspace

Test:

• create JS file with an unused variable.
• no ESLint error and no window message should appear.
• the ESLint output channel should contain a message like:

[Warn  - 3:14:29 PM] No ESLint configuration (e.g .eslintrc) found for file: extension.js
File will not be validated. Consider running the 'Create .eslintrc.json file' command.

• Run F1 > 'Create .eslintrc.json file'
• Ensure that the JS file is validated and a warning is shown for the unused var.

[octref]

Other than #12808 works great!