Test: ESLint: don't lint when there are config errors

[chrmarti]

Various issues fixed for the ESLint extension (see https://github.com/Microsoft/vscode-eslint)

• any OS - @roblourens

Complexity: 3

Setup:

• Install eslint-extension@latest
• create a new workspace and change dir into it
• npm install eslint
• open workspace
• F1 > ESLint: Create .eslintrc.json file

Test:

• create a JS file and add some content that produces errors. For example unused vars.
• open the .eslintrc.json file
• remove a '{' to make it a broken json
• open the Output channel 'ESLint'. Ensure that the channel contains a message about a error in the json. Also ensure that the output channel doesn't pop to front if not already active.
• close the .eslintrc.json file
• reload the workspace and open the js file again
• Ensure that you get a window message informing you about the broken '.eslintrc.json' file.
• type in the JS file. Ensure that no window message is shown.
• The rule is as follows: if the .eslintrc.json file is open not window message is shown. If the file is not open the message is shown once as long as the specific kind of error exists in the file. If the file gets valid again or other kind of errors get introduce those are shown as well.
• try to create other kind of errors (e.g. eslint plugin not found, ....). Ensure that they behave like the rule above.