Add linter error for `!x` conditions that can't be `undefined` or `null` or `string`

Created by: olafurpg

Issue type

Internal request

Problem description

Our current linter rules don't error on the following pattern

const x: string[] = []
if (!x) { ... }

It would be nice if our linter setup reported an error that the !x condition cannot be false because empty arrays are truthy in JavaScript.

Context

https://sourcegraph.slack.com/archives/C01LTKUHRL3/p1661336245339599

Steps to reproduce

No response

Impact

The PR #40610 introduced a regression causing an incident on sourcegraph.com where syntax highlighting stopped working (see INC-140). The PR included a change that was supposed to be a refactoring of how we parse a string | undefined into a Occurrence[] data structure, but the refactoring broke syntax highlighting because the value of occurrences in a condition if (!occurrences) changed from undefined to [].

Additional details

No response

Assigning labels

• If this issue will require input from designers in order to complete, please assign the label needs-design.

/cc @taylorsperry @jasongornall