refactor: add deno_file op crate (#10019)

Also enables WPT for FileReader.

op_crates/file/lib.deno_file.d.ts

@@ -0,0 +1,40 @@
+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+
+/// <reference no-default-lib="true" />
+/// <reference lib="esnext" />
+
+type BlobPart = BufferSource | Blob | string;
+
+interface BlobPropertyBag {
+  type?: string;
+  endings?: "transparent" | "native";
+}
+
+/** A file-like object of immutable, raw data. Blobs represent data that isn't necessarily in a JavaScript-native format. The File interface is based on Blob, inheriting blob functionality and expanding it to support files on the user's system. */
+declare class Blob {
+  constructor(blobParts?: BlobPart[], options?: BlobPropertyBag);
+
+  readonly size: number;
+  readonly type: string;
+  arrayBuffer(): Promise<ArrayBuffer>;
+  slice(start?: number, end?: number, contentType?: string): Blob;
+  stream(): ReadableStream<Uint8Array>;
+  text(): Promise<string>;
+}
+
+interface FilePropertyBag extends BlobPropertyBag {
+  lastModified?: number;
+}
+
+/** Provides information about files and allows JavaScript in a web page to
+ * access their content. */
+declare class File extends Blob {
+  constructor(
+    fileBits: BlobPart[],
+    fileName: string,
+    options?: FilePropertyBag,
+  );
+
+  readonly lastModified: number;
+  readonly name: string;
+}