move dropcursor and gapcursor to its own package

packages/extension-gapcursor/index.ts

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