src/vs/workbench/api/common/shared/dataTransferCache.ts/DataTransferCache/resolveDropFileData
class DataTransferCache:	async resolveDropFileData(requestId: number, dataItemId: string): Promise<VSBuffer> {
		const entry = this.dataTransfers.get(requestId);
		if (!entry) {
			throw new Error('No data transfer found');
		}

		const item = entry.find(x => x.id === dataItemId);
		if (!item) {
			throw new Error('No item found in data transfer');
		}

		const file = item.asFile();
		if (!file) {
			throw new Error('Found data transfer item is not a file');
		}

		return VSBuffer.wrap(await file.data());
	}