Move `listener-collection.js` to `src/shared`

`src/shared/port-rpc.js` depended on
`src/annotation/util/listener-collection.js`. Files in the `src/shared`
folder should not have dependencies on `src/annotation`.

`ListenerCollection` is a very general utility and the placement in
`src/shared` seems correct.

I took the opportunity to reorder the imports according to our
conventions.

src/annotator/bucket-bar.js

 import { render } from 'preact';
-import Buckets from './components/Buckets';
 
+import { ListenerCollection } from '../shared/listener-collection';
+
+import Buckets from './components/Buckets';
 import { anchorBuckets } from './util/buckets';
-import { ListenerCollection } from './util/listener-collection';
 
 /**
  * @typedef BucketBarOptions

src/annotator/guest.js

-import { Adder } from './adder';
-import { CrossFrame } from './cross-frame';
-import { HTMLIntegration } from './integrations/html';
-import { PDFIntegration } from './integrations/pdf';
+import { ListenerCollection } from '../shared/listener-collection';
 
+import { Adder } from './adder';
 import { TextRange } from './anchoring/text-range';
+import { CrossFrame } from './cross-frame';
 import {
   getHighlightsContainingNode,
   highlightRange,
@@ -12,10 +11,11 @@ import {
   setHighlightsFocused,
   setHighlightsVisible,
 } from './highlighter';
+import { HTMLIntegration } from './integrations/html';
+import { PDFIntegration } from './integrations/pdf';
 import * as rangeUtil from './range-util';
 import { SelectionObserver } from './selection-observer';
 import { normalizeURI } from './util/url';
-import { ListenerCollection } from './util/listener-collection';
 
 /**
  * @typedef {import('./util/emitter').EventBus} EventBus

src/annotator/integrations/pdf.js

 import debounce from 'lodash.debounce';
 import { render } from 'preact';
 
+import { ListenerCollection } from '../../shared/listener-collection';
 import {
   RenderingStates,
   anchor,
@@ -10,7 +11,6 @@ import {
 import { isInPlaceholder, removePlaceholder } from '../anchoring/placeholder';
 import WarningBanner from '../components/WarningBanner';
 import { createShadowRoot } from '../util/shadow-root';
-import { ListenerCollection } from '../util/listener-collection';
 import { offsetRelativeTo, scrollElement } from '../util/scroll';
 
 import { PDFMetadata } from './pdf-metadata';

src/annotator/selection-observer.js

-import { ListenerCollection } from './util/listener-collection';
+import { ListenerCollection } from '../shared/listener-collection';
 
 /**
  * Return the current selection or `null` if there is no selection or it is empty.

src/annotator/sidebar.js

 import Hammer from 'hammerjs';
 
+import events from '../shared/bridge-events';
+import { ListenerCollection } from '../shared/listener-collection';
+
 import annotationCounts from './annotation-counts';
-import sidebarTrigger from './sidebar-trigger';
+import BucketBar from './bucket-bar';
 import { createSidebarConfig } from './config/sidebar';
-import events from '../shared/bridge-events';
 import features from './features';
-
+import sidebarTrigger from './sidebar-trigger';
 import { ToolbarController } from './toolbar';
 import { createShadowRoot } from './util/shadow-root';
-import BucketBar from './bucket-bar';
-import { ListenerCollection } from './util/listener-collection';
 
 /**
  * @typedef {import('./guest').default} Guest

src/shared/port-rpc.js

-import { ListenerCollection } from '../annotator/util/listener-collection';
+import { ListenerCollection } from './listener-collection';
 
 /*
   This module was adapted from `index.js` in https://github.com/substack/frame-rpc.

src/annotator/util/test/listener-collection-test.js → src/shared/test/listener-collection-test.js

-import { ListenerCollection } from '../../util/listener-collection';
+import { ListenerCollection } from '../listener-collection';
 
 describe('ListenerCollection', () => {
   let listeners;

src/sidebar/components/ThreadList.js

 import { useEffect, useLayoutEffect, useMemo, useState } from 'preact/hooks';
 import debounce from 'lodash.debounce';
 
-import { useStoreProxy } from '../store/use-store';
+import { ListenerCollection } from '../../shared/listener-collection';
 import { isHighlight } from '../helpers/annotation-metadata';
-import { getElementHeightWithMargins } from '../util/dom';
 import {
   calculateVisibleThreads,
   THREAD_DIMENSION_DEFAULTS,
 } from '../helpers/visible-threads';
+import { useStoreProxy } from '../store/use-store';
+import { getElementHeightWithMargins } from '../util/dom';
 
 import ThreadCard from './ThreadCard';
-import { ListenerCollection } from '../../annotator/util/listener-collection';
 
 /** @typedef {import('../helpers/build-thread').Thread} Thread */
 

src/sidebar/util/observe-element-size.js

-import { ListenerCollection } from '../../annotator/util/listener-collection';
+import { ListenerCollection } from '../../shared/listener-collection';
 
 /**
  * Watch for changes in the size (`clientWidth` and `clientHeight`) of