feat(editor): eslint/tsconfig migration + type fixes

@robonen/editor: migrate to eslint flat config + composite tsconfig; fix
convergence test type annotations.

vue/editor/src/marks/italic.ts

@@ -0,0 +1,12 @@
+import { defineMark } from '../registry';
+
+export const italic = defineMark({
+  type: 'italic',
+  spec: {
+    inclusive: true,
+    rank: 2,
+    toDOM: () => ['em', 0],
+    parseDOM: [{ tag: 'em' }, { tag: 'i' }],
+  },
+  meta: { title: 'Italic', icon: 'italic', hotkey: 'Mod-i' },
+});