This updates ESLint and our shared eslint-config-openlayers to use Prettier. Most formatting changes were automatically applied with this:
npm run lint -- --fix
A few manual changes were required:
* In `examples/offscreen-canvas.js`, the `//eslint-disable-line` comment needed to be moved to the appropriate line to disable the error about the `'worker-loader!./offscreen-canvas.worker.js'` import.
* In `examples/webpack/exapmle-builder.js`, spaces could not be added after a couple `function`s for some reason. While editing this, I reworked `ExampleBuilder` to be a class.
* In `src/ol/format/WMSGetFeatureInfo.js`, the `// @ts-ignore` comment needed to be moved down one line so it applied to the `parsersNS` argument.
Instead of having `ol.events.Key` be a listener object or an array of listener objects, it should be less error prone to have it just be a single listener object.
To avoid using too many functions with multiple return types, the `ol.events.*` functions for registering and unregistering listeners no longer accept an array of event types (and only a single key is returned when registering).
To make it convenient for users to register multiple listeners at once, the `observable.on()` method accepts an array of event types. Internally in the library, we should use the less risky `ol.events.listen()`.
