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-ui-core/src/RenderHost.tsx

@@ -66,8 +66,13 @@ export interface RenderHost {
     message?: string;
     title?: string;
   }): Promise<string | undefined>;
+  /**
+   * @deprecated
+   * TODO: Remove in favor of "importFile"
+   */
   showOpenDialog?: FlipperLib['showOpenDialog'];
   showSelectDirectoryDialog?(defaultPath?: string): Promise<string | undefined>;
+  importFile: FlipperLib['importFile'];
   exportFile: FlipperLib['exportFile'];
   /**
    * @returns
@@ -106,6 +111,9 @@ if (process.env.NODE_ENV === 'test') {
       return '';
     },
     writeTextToClipboard() {},
+    async importFile() {
+      return undefined;
+    },
     async exportFile() {
       return undefined;
     },