Stabilize playwright tests by making the left panel constant width (#33451)

* Move css injection to panel.ts

- Inject css on event

* Upgrade package

* Fix playwright tests

* Remove RR instead of masking it

* Fix wrong import

* Fix playwright tests

* Fix more playwright tests

* Catch error and add comment

packages/shared-components/package.json

@@ -78,7 +78,7 @@
         "matrix-web-i18n": "catalog:",
         "react-blurhash": "^0.3.0",
         "react-merge-refs": "^3.0.2",
-        "react-resizable-panels": "4.7.2",
+        "react-resizable-panels": "4.9.0",
         "react-virtuoso": "^4.14.0",
         "temporal-polyfill": "^0.3.0"
     },