fix(c9): use 'fs' for c9 when calling writeFile (#4416)

Problem: the C9 stub for the vscode api's writeFile does not support
writing outside of the workspace dir, which can happen when adding new
IAM credentials.

Solution: Fall back to a standard fs library for C9.

#### Testing
Tested on C9

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## License

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.

Co-authored-by: aws-toolkit-automation <>

Author: hayemaxi

packages/toolkit/src/srcShared/fs.ts

@@ -105,6 +105,13 @@ export class FileSystemCommon {
      */
     async writeFile(path: Uri | string, data: string | Uint8Array): Promise<void> {
         path = FileSystemCommon.getUri(path)
+
+        // vscode.workspace.writeFile is stubbed in C9 has limited functionality,
+        // e.g. cannot write outside of open workspace
+        if (isCloud9()) {
+            await fsPromises.writeFile(path.fsPath, FileSystemCommon.asArray(data))
+            return
+        }
         return fs.writeFile(path, FileSystemCommon.asArray(data))
     }