fix(RCTImageLoader): Adds requiresMainQueueSetup to fix v0.52

Summary:
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In react-native v0.52 this warning shows:
```
"RCTImageLoader requires main queue setup
since it overrides `init` but doesn't implement `requiresMainQueueSetup`".
```
This removes the warning by implementing `requiresMainQueueSetup` on RCTImageLoader

* Create new react-native project
* Enable Remote JS Debugging
* Should see no warning regarding RCTImageLoader requiring main queue setup

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  CATEGORY
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 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
 [ANDROID] [BUGFIX] [TextInput] - Did a thing to TextInput
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[IOS] [BUGFIX] [Libraries/Image/RCTImageLoader.m] - Implements `requiresMainQueueSetup`
Closes facebook#17679

Reviewed By: shergin

Differential Revision: D7159601

Pulled By: fkgozali

fbshipit-source-id: e17bae67f4005d2c9ddd0d3701506521f3cac152

Libraries/Image/RCTImageLoader.m

@@ -58,6 +58,11 @@ - (instancetype)init
   return [self initWithRedirectDelegate:nil];
 }
 
++ (BOOL)requiresMainQueueSetup
+{
+    return NO;
+}
+
 - (instancetype)initWithRedirectDelegate:(id<RCTImageRedirectProtocol>)redirectDelegate
 {
     if (self = [super init]) {