Add Automated Test for Options

[karlhorky]

Add an automated test to test one of the options (eg. amVim.useSystemClipboard introduced in #260).

[alisonatwork]

It has been hard for us to write automated tests that rely on certain values being set in the user settings. For example, I was not able to write repeatable tests for wrapped line functionality (#116) because they would depend on setting a consistent wrapped line value that was the same in CI as local. But it looks like the recent September update of VS Code might allow us to do this, by setting up a special profile with its own settings just for testing: https://code.visualstudio.com/updates/v1_72#_extension-debugging-in-a-clean-environment

I need more time to look into this, but just wanted to drop a comment here to remind us in the future when we take a look at this ticket.