src/vs/workbench/api/common/extHostFileSystem.ts/ExtHostFileSystem/$open
class ExtHostFileSystem:	$open(handle: number, resource: UriComponents, opts: files.IFileOpenOptions): Promise<number> {
		const provider = this._getFsProvider(handle);
		if (!provider.open) {
			throw new Error('FileSystemProvider does not implement "open"');
		}
		return Promise.resolve(provider.open(URI.revive(resource), opts));
	}