Dialog management cleanup

Summary:
This diff moves the dialogs

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To use the imperative dialog APIs, rather then organising them through reducers which adds a lot of indirection which isn't really needed but hard to follow.

Reviewed By: passy

Differential Revision: D30192002

fbshipit-source-id: ba38b2e700da3e442653786448fcbf85074981ad

desktop/flipper-plugin/src/ui/Dialog.tsx

@@ -13,7 +13,8 @@ import React from 'react';
 import {renderReactRoot} from '../utils/renderReactRoot';
 import {Layout} from './Layout';
 import {Spinner} from './Spinner';
-type DialogResult<T> = Promise<false | T> & {close: () => void};
+
+export type DialogResult<T> = Promise<false | T> & {close: () => void};
 
 type BaseDialogOptions = {
   title: string;
@@ -104,6 +105,36 @@ export const Dialog = {
     );
   },
 
+  /**
+   * Shows an item in the modal stack, but without providing any further UI, like .show does.
+   */
+  showModal<T = void>(
+    fn: (hide: (result?: T) => void) => React.ReactElement,
+  ): DialogResult<T> {
+    let cancel: () => void;
+
+    return Object.assign(
+      new Promise<false | T>((resolve) => {
+        renderReactRoot((hide) => {
+          cancel = () => {
+            hide();
+            resolve(false);
+          };
+
+          return fn((result?: T) => {
+            hide();
+            resolve(result ?? false);
+          });
+        });
+      }),
+      {
+        close() {
+          cancel();
+        },
+      },
+    );
+  },
+
   confirm({
     message,
     onConfirm,