add Select All to editor context menu

src/components/Editor.tsx

@@ -158,6 +158,12 @@ class Editor extends React.Component<EditorProps> {
                     icon="clipboard"
                     label={isMacOS() ? 'Cmd-V' : 'Ctrl-V'}
                 />
+                <MenuItem
+                    onClick={() => this.editor?.selectAll()}
+                    text={i18n.translate(EditorStringId.SelectAll)}
+                    icon="blank"
+                    label={isMacOS() ? 'Cmd-A' : 'Ctrl-A'}
+                />
                 <MenuDivider />
                 <MenuItem
                     onClick={(): void => this.editor?.undo()}

src/components/editor-i18n.en.json

@@ -3,6 +3,7 @@
         "placeholder": "Write your program here...",
         "copy": "Copy",
         "paste": "Paste",
+        "selectAll": "Select All",
         "undo": "Undo",
         "redo": "Redo"
     }

src/components/editor-i18n.ts

@@ -7,6 +7,7 @@ export enum EditorStringId {
     Placeholder = 'editor.placeholder',
     Copy = 'editor.copy',
     Paste = 'editor.paste',
+    SelectAll = 'editor.selectAll',
     Undo = 'editor.undo',
     Redo = 'editor.redo',
 }