src/vs/workbench/contrib/files/browser/fileActions.ts/uploadFileHandler
const uploadFileHandler = async (accessor: ServicesAccessor) => {
	const explorerService = accessor.get(IExplorerService);
	const instantiationService = accessor.get(IInstantiationService);

	const context = explorerService.getContext(true);
	const element = context.length ? context[0] : explorerService.roots[0];

	const files = await triggerUpload();
	if (files) {
		const browserUpload = instantiationService.createInstance(BrowserFileUpload);
		return browserUpload.upload(element, files);
	}
};