feat(core): drop doc onto split view (#9487)

fix AF-2068, AF-2069, AF-1175, AF-2061, AF-2079, AF-2034, AF-2080, AF-1960, AF-2081

1. replace `dnd-kit` with `@atlaskit/pragmatic-drag-and-drop`
2. allow creating split views by drag & drop the following
   a. WorkbenchLinks (route links), like journals, trash, all docs
   b. doc refs
   c. tags/collection
3. style adjustments to split view
4. remove split view's feature flag and make it GA for electron

https://github.com/user-attachments/assets/6a3e4a25-faa2-4215-8eb0-983f44db6e8c

packages/frontend/core/package.json

@@ -20,9 +20,6 @@
     "@blocksuite/icons": "2.2.1",
     "@capacitor/app": "^6.0.2",
     "@capacitor/browser": "^6.0.4",
-    "@dnd-kit/core": "^6.3.1",
-    "@dnd-kit/modifiers": "^9.0.0",
-    "@dnd-kit/sortable": "^10.0.0",
     "@dotlottie/player-component": "^2.7.12",
     "@emotion/cache": "^11.14.0",
     "@emotion/react": "^11.14.0",