Update center toggle focus mode icon with gl-icon

MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/43888

app/assets/javascripts/boards/icons/fullscreen_collapse.svg

-<svg width="17" height="17" viewBox="0 0 17 17" xmlns="http://www.w3.org/2000/svg"><path d="M.147 15.496l2.146-2.146-1.286-1.286a.55.55 0 0 1-.125-.616c.101-.238.277-.357.527-.357h4a.55.55 0 0 1 .402.17.55.55 0 0 1 .17.401v4c0 .25-.12.426-.358.527-.232.101-.437.06-.616-.125l-1.286-1.286-2.146 2.146-1.428-1.428zM14.996.646l1.428 1.43-2.146 2.145 1.286 1.286c.185.179.226.384.125.616-.101.238-.277.357-.527.357h-4a.55.55 0 0 1-.402-.17.55.55 0 0 1-.17-.401v-4c0-.25.12-.426.358-.527a.553.553 0 0 1 .616.125l1.286 1.286L14.996.647zm-13.42 0L3.72 2.794l1.286-1.286a.55.55 0 0 1 .616-.125c.238.101.357.277.357.527v4a.55.55 0 0 1-.17.402.55.55 0 0 1-.401.17h-4c-.25 0-.426-.12-.527-.358-.101-.232-.06-.437.125-.616l1.286-1.286L.147 2.075 1.575.647zm14.848 14.85l-1.428 1.428-2.146-2.146-1.286 1.286c-.179.185-.384.226-.616.125-.238-.101-.357-.277-.357-.527v-4a.55.55 0 0 1 .17-.402.55.55 0 0 1 .401-.17h4c.25 0 .426.12.527.358a.553.553 0 0 1-.125.616l-1.286 1.286 2.146 2.146z" fill-rule="evenodd"/></svg>

app/assets/javascripts/boards/icons/fullscreen_expand.svg

-<svg width="15" height="15" viewBox="0 0 15 15" xmlns="http://www.w3.org/2000/svg"><path d="M8.591 5.056l2.147-2.146-1.286-1.286a.55.55 0 0 1-.125-.616c.101-.238.277-.357.527-.357h4a.55.55 0 0 1 .402.17.55.55 0 0 1 .17.401v4c0 .25-.12.426-.358.527-.232.101-.437.06-.616-.125l-1.286-1.286-2.146 2.147-1.429-1.43zM5.018 8.553l1.429 1.43L4.3 12.127l1.286 1.286c.185.179.226.384.125.616-.101.238-.277.357-.527.357h-4a.55.55 0 0 1-.402-.17.55.55 0 0 1-.17-.401v-4c0-.25.12-.426.358-.527a.553.553 0 0 1 .616.125L2.872 10.7l2.146-2.147zm4.964 0l2.146 2.147 1.286-1.286a.55.55 0 0 1 .616-.125c.238.101.357.277.357.527v4a.55.55 0 0 1-.17.402.55.55 0 0 1-.401.17h-4c-.25 0-.426-.12-.527-.358-.101-.232-.06-.437.125-.616l1.286-1.286-2.147-2.146 1.43-1.429zM6.447 5.018l-1.43 1.429L2.873 4.3 1.586 5.586c-.179.185-.384.226-.616.125-.238-.101-.357-.277-.357-.527v-4a.55.55 0 0 1 .17-.402.55.55 0 0 1 .401-.17h4c.25 0 .426.12.527.358a.553.553 0 0 1-.125.616L4.3 2.872l2.147 2.146z" fill-rule="evenodd"/></svg>

app/assets/javascripts/boards/toggle_focus.js

 import $ from 'jquery';
 import Vue from 'vue';
-import collapseIcon from './icons/fullscreen_collapse.svg';
-import expandIcon from './icons/fullscreen_expand.svg';
+import { GlIcon } from '@gitlab/ui';
 
 export default (ModalStore, boardsStore) => {
   const issueBoardsContent = document.querySelector('.content-wrapper > .js-focus-mode-board');
 
   return new Vue({
     el: document.getElementById('js-toggle-focus-btn'),
+    components: {
+      GlIcon,
+    },
     data: {
       modal: ModalStore.store,
       store: boardsStore.state,
@@ -32,12 +34,7 @@ export default (ModalStore, boardsStore) => {
           title="Toggle focus mode"
           ref="toggleFocusModeButton"
           @click="toggleFocusMode">
-          <span v-show="isFullscreen">
-            ${collapseIcon}
-          </span>
-          <span v-show="!isFullscreen">
-            ${expandIcon}
-          </span>
+          <gl-icon :name="isFullscreen ? 'minimize' : 'maximize'" />
         </a>
       </div>
     `,

changelogs/unreleased/258677-center-toggle-focus-mode-icon.yml

+---
+title: Update toggle focus mode icon to gl-icon
+merge_request: 43888
+author:
+type: changed