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/highlight.ts

@@ -0,0 +1,12 @@
+import { defineMark } from '../registry';
+
+export const highlight = defineMark({
+  type: 'highlight',
+  spec: {
+    inclusive: true,
+    rank: 5,
+    toDOM: () => ['mark', 0],
+    parseDOM: [{ tag: 'mark' }],
+  },
+  meta: { title: 'Highlight', icon: 'highlighter' },
+});