fix: Ensure filename is available for diff rendering in write-file

This commit resolves a bug where the `write-file` operation could fail to render content due to a missing filename.

The fix involves:
- Ensuring `fileName` is consistently passed to `DiffRenderer.tsx` through `ToolConfirmationMessage.tsx`, `ToolMessage.tsx`, and `useGeminiStream.ts`.
- Modifying `edit.ts` and `write-file.ts` to include `fileName` in the `FileDiff` object.
- Expanding the `FileDiff` interface in `tools.ts` to include `fileName`.

Additionally, this commit enhances the diff rendering by:
- Adding syntax highlighting based on file extension in `DiffRenderer.tsx`.
- Adding more language mappings to `getLanguageFromExtension` in `DiffRenderer.tsx`.
- Added lots of tests for all the above.

Fixes https://b.corp.google.com/issues/418125982

package.json

@@ -16,7 +16,7 @@
     "debug": "NODE_ENV=development DEBUG=1 scripts/start.sh",
     "lint:fix": "eslint . --fix",
     "lint": "eslint . --ext .ts,.tsx",
-    "typecheck": "tsc --noEmit --jsx react-jsx",
+    "typecheck": "npm run typecheck --workspaces --if-present",
     "format": "prettier --write .",
     "preflight": "npm run format --workspaces --if-present && npm run lint && npm run test --workspaces --if-present",
     "auth:npm": "npx google-artifactregistry-auth",