These modules have default exports and are imported by CoffeeScript
modules. Since we use CoffeeScript 1.x which doesn't support
`import`/`export` syntax, we use destructuring to access the default
export.

This is necessary to support mocking the JS generated by the following
CoffeeScript syntax:

```
{ default: FooBar } = require("./foo-bar")
```

This will be used in CoffeeScript modules that import ES modules with
default exports.

Convert src/shared/{polyfills, test, settings.js} to ES modules

Add `permissions` util and remove permissions-init logic from components

Convert all the modules under src/shared to ES modules except for those
which:

 1. Would have a default export if converted to an ES module AND
 2. Are imported by a module still written in CoffeeScript in src/annotator/

For modules which meet these criteria there is some additional work
required to make the tests for the CoffeeScript modules still work after
the conversion.

Migrate “modern” components away from using the `permissions` service
and instead use the `permissions` util.

Note: `permissions` service will hang around until the old `annotation`
controller is gone fully

- Remove permissions init from `annotation`, `AnnotationOmega`
- Add permissions init, via util and state, to `annotations` store module
- Remove unused methods from `permissions` service

Copy functionality of `permissions` service minus `localStorage`
dependency into a new util; add `isPrivate` method for convenience.

Add an `align-items` rule to the focused-mode button

Add `defaults` store module and `persistedDefaults` service

Add an alignment rule to CSS so that button text aligns vertical
center in Firefox.

Add a new store module for managing state of client-side defaults
and a new service for a) retrieving those values from where they
were persisted on initialization and b) subscribing to the store
to watch for changes on those defaults—and persisting those changes.

Update the `permissions` service to get/set its default annotation
privacy level through the store instead of directly through
`localStorage`.

Convert additional src/annotator/ modules to ES modules

This converts all modules except those which:

 1) Are written in CoffeeScript OR

 2) Are written in JS AND have a default export AND are imported from a
    module written in CoffeeScript.

    This last case is a bit more complex to handle and needs a little
    investigation or a decision to punt it to after the CoffeeScript =>
    JS conversion is complete

Convert most modules in src/annotator to ES modules

In preparation for conversion to an ES module, hoist an import to the
top of the file.

This module has no tests :(

These were not converted in the previous commit as they were not
top-level statements in the file.

Convert text highlighter to JS

Convert src/boot to ES modules

 - Add missing parameter / return type docs
 - Update a Chrome bug tracker issue link

Remove the highlighter implementation abstraction layer in
src/annotator/highlighter since only one type of highlighter was ever
implemented and convert the one implementation in
src/annotator/highlighter/dom-wrap-highlighter/index.coffee to JS as
src/annotator/highlighter.js.

Convert remaining sidebar files to ES modules

Use the convert-to-es-modules script to convert the remaining
CommonJS/Node module files in src/sidebar/ to ES modules.

Convert src/sidebar/directives to ES modules

This directory is likely to go away soon as part of the Angular =>
Preact migration.

Nevertheless, I used the convert-to-es-modules script on it to convert
to ES modules so we can complete that migration first.

This is mostly to make it easier for the convert-to-es-modules script to
preserve comments when these modules are converted to ES modules.
However it may also be useful for debugging.

Convert src/sidebar/store to ES modules

This import should be hoisted to the top level of the module but a naive change to do this did not work. I suspect this relates to the circular nature of the
import, but it needs investigating. This change enables the code to
continue working until then.

`$imports` is now a separate named export rather than a property of the
default export.

After converting the module under test to an ES module the mocked functions are now properties of the default export rather than named exports.