Implement fs.readFile / fs.writeFile

Summary: Per title. Made an explicit distinction between binary and non binary files, since they need to be encoded differently. This keeps both the implementation and API simpler (in terms of overloading / type checking)

Reviewed By: aigoncharov

Differential Revision: D33016031

fbshipit-source-id: 3c99956eb016849a908a171d88a7a64a88b76268

desktop/flipper-plugin/src/plugin/FlipperLib.tsx

@@ -66,6 +66,17 @@ export type RemoteServerContext = {
     copyFile(src: string, dest: string, flags?: number): Promise<void>;
     stat(path: string): Promise<FSStatsLike>;
     readlink(path: string): Promise<string>;
+    readFile(
+      path: string,
+      options?: {encoding?: BufferEncoding},
+    ): Promise<string>;
+    readFileBinary(path: string): Promise<Uint8Array>; // No Buffer, which is not a browser type
+    writeFile(
+      path: string,
+      contents: string,
+      options?: {encoding?: BufferEncoding},
+    ): Promise<void>;
+    writeFileBinary(path: string, contents: Uint8Array): Promise<void>;
   };
   downloadFile(
     url: string,