feat(lexical): support local image data URLs

Allow the image insertion dialog to select a local image and embed it as a Base64 data URL, while retaining URL-based insertion and leaving video URL-only.

Extract shared abortable FileReader handling for clipboard uploads and dialog selection; add English and Simplified Chinese messages plus an interaction test covering file selection through insertion.

packages/lexical/src/advanced-features.test.tsx

@@ -6,6 +6,7 @@ import {
   render,
   screen,
   waitFor,
+  within,
 } from "@testing-library/react"
 import { afterEach, describe, expect, it } from "vitest"
 
@@ -190,6 +191,52 @@ describe("Lexical advanced actions", () => {
     expect((caption as HTMLTextAreaElement).value).toBe("Updated caption")
   })
 
+  it("reads an image selected from the insert dialog as a Base64 data URL", async () => {
+    const { container } = render(
+      <LexicalRoot value="<p>before</p>" onChange={() => undefined}>
+        <LexicalActions>
+          <Image />
+        </LexicalActions>
+        <LexicalFixedToolbar />
+        <LexicalContent />
+      </LexicalRoot>
+    )
+
+    fireEvent.click(screen.getByRole("button", { name: "Insert image" }))
+    const dialog = await screen.findByRole("dialog")
+
+    const file = new File([new Uint8Array([137, 80, 78, 71])], "local.png", {
+      type: "image/png",
+    })
+    fireEvent.change(within(dialog).getByLabelText("Image file"), {
+      target: { files: [file] },
+    })
+
+    const urlInput = within(dialog).getByRole("textbox", {
+      name: "Image URL",
+    })
+    await waitFor(() => {
+      expect((urlInput as HTMLInputElement).value).toMatch(
+        /^data:image\/png;base64,/
+      )
+    })
+
+    fireEvent.change(
+      within(dialog).getByRole("textbox", { name: "Alternative text" }),
+      {
+        target: { value: "Local image" },
+      }
+    )
+    fireEvent.submit(dialog.querySelector("form")!)
+
+    await waitFor(() => {
+      expect(
+        screen.getByRole("img", { name: "Local image" }).getAttribute("src")
+      ).toMatch(/^data:image\/png;base64,/)
+    })
+    expect(container.querySelector("figure")).not.toBeNull()
+  })
+
   it("lets a custom Video control insert a video through execute", async () => {
     const { container } = render(
       <LexicalRoot value="<p>before</p>" onChange={() => undefined}>