Fix up NativeDialogManagerAndroid PR

Summary:
This diff has three changes:
1. Remove all references to `Stringish` from `NativeDialogManagerAndroid`. (All Fbt objects expose a `.toString` method we could call).
2. Make sure that we only access `DialogManagerAndroid` through `NativeDialogManagerAndroid`.
3. Removed a bunch of `$FlowFixMes` in the files I touched. Probably not the best idea to bite into this cleanup on this diff, but what's done is done.

Since this diff is fairly large, I've commented on parts of it I thought were note-worthy. I've also commented on the changes I had to make to fix flow after removing the `$FlowFixMe`s.

Reviewed By: PeteTheHeat

Differential Revision: D16428855

fbshipit-source-id: 0e6daf2957f4b086ebb1e78e0a59930668c65576

Libraries/FBReactNativeSpec/FBReactNativeSpec/FBReactNativeSpec.h

@@ -739,10 +739,10 @@ namespace JS {
   namespace NativeDialogManagerAndroid {
     struct DialogOptions {
       NSString *title() const;
-      id<NSObject> _Nullable message() const;
-      id<NSObject> _Nullable buttonPositive() const;
-      id<NSObject> _Nullable buttonNegative() const;
-      id<NSObject> _Nullable buttonNeutral() const;
+      NSString *message() const;
+      NSString *buttonPositive() const;
+      NSString *buttonNegative() const;
+      NSString *buttonNeutral() const;
       folly::Optional<facebook::react::LazyVector<NSString *>> items() const;
       folly::Optional<bool> cancelable() const;
 
@@ -2463,25 +2463,25 @@ inline NSString *JS::NativeDialogManagerAndroid::DialogOptions::title() const
   id const p = _v[@"title"];
   return RCTBridgingToString(p);
 }
-inline id<NSObject> _Nullable JS::NativeDialogManagerAndroid::DialogOptions::message() const
+inline NSString *JS::NativeDialogManagerAndroid::DialogOptions::message() const
 {
   id const p = _v[@"message"];
-  return p;
+  return RCTBridgingToString(p);
 }
-inline id<NSObject> _Nullable JS::NativeDialogManagerAndroid::DialogOptions::buttonPositive() const
+inline NSString *JS::NativeDialogManagerAndroid::DialogOptions::buttonPositive() const
 {
   id const p = _v[@"buttonPositive"];
-  return p;
+  return RCTBridgingToString(p);
 }
-inline id<NSObject> _Nullable JS::NativeDialogManagerAndroid::DialogOptions::buttonNegative() const
+inline NSString *JS::NativeDialogManagerAndroid::DialogOptions::buttonNegative() const
 {
   id const p = _v[@"buttonNegative"];
-  return p;
+  return RCTBridgingToString(p);
 }
-inline id<NSObject> _Nullable JS::NativeDialogManagerAndroid::DialogOptions::buttonNeutral() const
+inline NSString *JS::NativeDialogManagerAndroid::DialogOptions::buttonNeutral() const
 {
   id const p = _v[@"buttonNeutral"];
-  return p;
+  return RCTBridgingToString(p);
 }
 inline folly::Optional<facebook::react::LazyVector<NSString *>> JS::NativeDialogManagerAndroid::DialogOptions::items() const
 {

Libraries/NativeModules/specs/NativeDialogManagerAndroid.js

@@ -23,10 +23,10 @@ type DialogAction = string;
 type DialogButtonKey = number;
 export type DialogOptions = {|
   title?: string,
-  message?: Stringish,
-  buttonPositive?: Stringish,
-  buttonNegative?: Stringish,
-  buttonNeutral?: Stringish,
+  message?: string,
+  buttonPositive?: string,
+  buttonNegative?: string,
+  buttonNeutral?: string,
   items?: Array<string>,
   cancelable?: boolean,
 |};