Add duplicate button for mobile view (#1146)

* Add a icon for dulplication

* Add PanelComponent for duplication

* Add duplicate button for mobile

* Add styles for layout action buttons

* Add a translation for 'Actions'

* Show left action buttons only for desktop

* Add duplicate button at the bottom of mobile

It is provided depending on whether or not it is `multiElement` to maintain space between buttons.

src/actions/actionDuplicateSelection.tsx

@@ -0,0 +1,49 @@
+import React from "react";
+import { KEYS } from "../keys";
+import { register } from "./register";
+import { ExcalidrawElement } from "../element/types";
+import { duplicateElement } from "../element";
+import { isSomeElementSelected } from "../scene";
+import { ToolButton } from "../components/ToolButton";
+import { clone } from "../components/icons";
+import { t } from "../i18n";
+import { getShortcutKey } from "../utils";
+
+export const actionDuplicateSelection = register({
+  name: "duplicateSelection",
+  perform: (elements, appState) => {
+    return {
+      appState,
+      elements: elements.reduce(
+        (acc: Array<ExcalidrawElement>, element: ExcalidrawElement) => {
+          if (appState.selectedElementIds[element.id]) {
+            const newElement = duplicateElement(element, {
+              x: element.x + 10,
+              y: element.y + 10,
+            });
+            appState.selectedElementIds[newElement.id] = true;
+            delete appState.selectedElementIds[element.id];
+            return acc.concat([element, newElement]);
+          }
+          return acc.concat(element);
+        },
+        [],
+      ),
+      commitToHistory: true,
+    };
+  },
+  contextItemLabel: "labels.duplicateSelection",
+  keyTest: (event) => event[KEYS.CTRL_OR_CMD] && event.key === "d",
+  PanelComponent: ({ elements, appState, updateData }) => (
+    <ToolButton
+      type="button"
+      icon={clone}
+      title={`${t("labels.duplicateSelection")} ${getShortcutKey(
+        "CtrlOrCmd+D",
+      )}`}
+      aria-label={t("labels.duplicateSelection")}
+      onClick={() => updateData(null)}
+      visible={isSomeElementSelected(elements, appState)}
+    />
+  ),
+});