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

packages/cli/src/ui/hooks/useGeminiStream.ts

@@ -326,6 +326,7 @@ export const useGeminiStream = (
       if ('fileDiff' in originalDetails) {
         resultDisplay = {
           fileDiff: (originalDetails as ToolEditConfirmationDetails).fileDiff,
+          fileName: (originalDetails as ToolEditConfirmationDetails).fileName,
         };
       } else {
         resultDisplay = `~~${(originalDetails as ToolExecuteConfirmationDetails).command}~~`;
@@ -590,7 +591,7 @@ export const useGeminiStream = (
           addItem(
             {
               type: MessageType.ERROR,
-              text: `[Stream Error: ${getErrorMessage(error)}]`,
+              text: `[Stream Error: ${getErrorMessage(error) || 'Unknown error'}]`,
             },
             userMessageTimestamp,
           );