ESLint rules have been added to enforce our JSDoc conventions. These
rules were introduced by updating `@metamask/eslint-config` to v9.
Some of the rules have been disabled because the effort to fix all lint
errors was too high. It might be easiest to enable these rules one
directory at a time, or one rule at a time.
Most of the changes in this PR were a result of running
`yarn lint:fix`. There were a handful of manual changes that seemed
obvious and simple to make. Anything beyond that and the rule was left
disabled.
A propType error was showing up during e2e tests with a `testDev`
build. It was caused by `process.env.IN_TEST` being treated as a
boolean, when in fact it is either the string `'true'` or a boolean.
`IN_TEST` has been updated to always be a boolean. `loose-envify` has
no trouble injecting boolean values, so there's no reason to treat this
as a string.
