@types/vscode/index.d.ts is an idential re-export of src/vscode-dts/vscode.d.ts in https://github.com/microsoft/vscode. See https://github.com/microsoft/vscode/tree/main/build/azure-pipelines/publish-types for how these types are updated.
If you would like to contribute, please open an issue or a pull request there. Any code changes on @types/vscode without going through microsoft/vscode repo will risk being eliminated by microsoft's pipeline.