move dropcursor and gapcursor to its own package

packages/extension-dropcursor/index.ts

@@ -0,0 +1,18 @@
+import { createExtension } from '@tiptap/core'
+import { dropCursor } from 'prosemirror-dropcursor'
+
+const Dropcursor = createExtension({
+  addProseMirrorPlugins() {
+    return [
+      dropCursor(),
+    ]
+  },
+})
+
+export default Dropcursor
+
+declare module '@tiptap/core/src/Editor' {
+  interface AllExtensions {
+    Dropcursor: typeof Dropcursor,
+  }
+}