Remove fs.readFile from some plugins

Summary:
1. Remove fs.readFile from some plugins
2. Add "importFile" to FlipperLib and RenderHost

See D32492149 for context

Followups:

1. Decapitate Stella's sendToPhone
2. Decapitate crash reporter
3. Figure out how to approach navigation
4. Figure out how to approach FileSelector

Reviewed By: mweststrate

Differential Revision: D32496775

fbshipit-source-id: e150aa56a2c2c1eb12a4c03c801f76cd76485a9d

desktop/flipper-plugin/src/__tests__/api.node.tsx

@@ -97,6 +97,7 @@ test('Correct top level API exposed', () => {
       "ElementSearchResultSet",
       "ElementsInspectorElement",
       "ElementsInspectorProps",
+      "FileDescriptor",
       "FlipperLib",
       "HighlightManager",
       "Idler",

desktop/flipper-plugin/src/index.ts

@@ -37,6 +37,7 @@ export {
   FlipperLib,
   getFlipperLib,
   setFlipperLibImplementation as _setFlipperLibImplementation,
+  FileDescriptor,
 } from './plugin/FlipperLib';
 export {
   MenuEntry,

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

@@ -14,6 +14,11 @@ import {RealFlipperClient} from './Plugin';
 import {Notification} from './Notification';
 import {DetailSidebarProps} from '../ui/DetailSidebar';
 
+export interface FileDescriptor {
+  data: string;
+  name: string;
+}
+
 /**
  * This interface exposes all global methods for which an implementation will be provided by Flipper itself
  */
@@ -42,6 +47,20 @@ export interface FlipperLib {
       name: string;
     };
   }): Promise<string | undefined>;
+  /**
+   * @returns
+   * Imported file data.
+   * If user cancelled a file selection - undefined.
+   */
+  importFile(options: {
+    defaultPath?: string;
+    extensions?: string[];
+  }): Promise<FileDescriptor | undefined>;
+  /**
+   * @returns
+   * An exported file path (if available) or a file name.
+   * If user cancelled a file selection - undefined.
+   */
   exportFile(
     data: string,
     options?: {

desktop/flipper-plugin/src/test-utils/test-utils.tsx

@@ -380,6 +380,7 @@ export function createMockFlipperLib(options?: StartPluginOptions): FlipperLib {
     openLink: jest.fn(),
     showNotification: jest.fn(),
     exportFile: jest.fn(),
+    importFile: jest.fn(),
     paths: {
       appPath: process.cwd(),
       homePath: `/dev/null`,