Convert React context providers to TypeScript [don't squash!] GitOrigin-RevId: d92a91798286978410956ab791d73c17c5086d86
* Upgrade react-resizable-panels * Add FileTreeOpenProvider * Add OutlineProvider and OutlineContainer * Convert Outline tests to Cypress GitOrigin-RevId: afd9ae8190edf37642e36a4ffb331f1182c8982d