👍 Expose FileFormat and related functions

Author: lambdalisue

denops_std/buffer/mod.ts

@@ -1,2 +1,9 @@
 export * from "./buffer.ts";
 export * from "./decoration.ts";
+export {
+  assertFileFormat,
+  ensureFileFormat,
+  isFileFormat,
+  maybeFileFormat,
+} from "./fileformat.ts";
+export type { FileFormat } from "./fileformat.ts";