feat: retain seed on shift-paste (#6509)

thanks for the review 👍

src/tests/test-utils.ts

@@ -190,3 +190,24 @@ export const toggleMenu = (container: HTMLElement) => {
   // open menu
   fireEvent.click(container.querySelector(".dropdown-menu-button")!);
 };
+
+export const createPasteEvent = (
+  text:
+    | string
+    | /* getData function */ ((type: string) => string | Promise<string>),
+  files?: File[],
+) => {
+  return Object.assign(
+    new Event("paste", {
+      bubbles: true,
+      cancelable: true,
+      composed: true,
+    }),
+    {
+      clipboardData: {
+        getData: typeof text === "string" ? () => text : text,
+        files: files || [],
+      },
+    },
+  );
+};