Improvements and bugfixes

To initiate a new Studio without installing the CLI globally:

npm create sanity@latest

To upgrade a v3 Studio, run this command in its folder:

npm install sanity@latest

• Fixes potential typing issues caused by mismatched versions of @types/react-is
• Fixes issue where validation tooltips were clipped inside of the Portable Text editor
• Improves accessibility of list panes when using screen readers