Move IDE left sidebar init width to constant

**Why?**
- Helps encapsulate this magic number

app/assets/javascripts/ide/components/ide_side_bar.vue

@@ -9,7 +9,7 @@ import CommitForm from './commit_sidebar/form.vue';
 import IdeReview from './ide_review.vue';
 import SuccessMessage from './commit_sidebar/success_message.vue';
 import IdeProjectHeader from './ide_project_header.vue';
-import { leftSidebarViews } from '../constants';
+import { leftSidebarViews, LEFT_SIDEBAR_INIT_WIDTH } from '../constants';
 
 export default {
   components: {
@@ -33,11 +33,16 @@ export default {
       );
     },
   },
+  LEFT_SIDEBAR_INIT_WIDTH,
 };
 </script>
 
 <template>
-  <resizable-panel :initial-width="340" side="left" class="multi-file-commit-panel flex-column">
+  <resizable-panel
+    :initial-width="$options.LEFT_SIDEBAR_INIT_WIDTH"
+    side="left"
+    class="multi-file-commit-panel flex-column"
+  >
     <template v-if="loading">
       <div class="multi-file-commit-panel-inner">
         <div v-for="n in 3" :key="n" class="multi-file-loading-container">

app/assets/javascripts/ide/components/resizable_panel.vue

 <script>
 import { mapActions } from 'vuex';
 import PanelResizer from '~/vue_shared/components/panel_resizer.vue';
+import { DEFAULT_SIDEBAR_MIN_WIDTH } from '../constants';
 
 export default {
   components: {
@@ -14,7 +15,7 @@ export default {
     minSize: {
       type: Number,
       required: false,
-      default: 340,
+      default: DEFAULT_SIDEBAR_MIN_WIDTH,
     },
     side: {
       type: String,

app/assets/javascripts/ide/constants.js

@@ -4,6 +4,9 @@ export const MAX_WINDOW_HEIGHT_COMPACT = 750;
 export const MAX_TITLE_LENGTH = 50;
 export const MAX_BODY_LENGTH = 72;
 
+export const LEFT_SIDEBAR_INIT_WIDTH = 340;
+export const DEFAULT_SIDEBAR_MIN_WIDTH = 340;
+
 // File view modes
 export const FILE_VIEW_MODE_EDITOR = 'editor';
 export const FILE_VIEW_MODE_PREVIEW = 'preview';