Fabric: Lazy initialization of RCTSurfaceTouchHandler on the main thread

Summary:
RCTSurfaceTouchHandler is not a thread-safe object and must be used (and initialized) on the main thread. Therefore we need to move the initialization to `view` method which is guaranteed to be called on the main thread.

Changelog: [Internal] Fabric-specific internal change.

Reviewed By: sammy-SC

Differential Revision: D24290776

fbshipit-source-id: fc1f2f157599aff6fca053451f89bf7cca3c812a

React/Fabric/Surface/RCTFabricSurface.mm

@@ -58,8 +58,6 @@ using namespace facebook::react;
 
     _maximumSize = CGSizeMake(CGFLOAT_MAX, CGFLOAT_MAX);
 
-    _touchHandler = [RCTSurfaceTouchHandler new];
-
     _stage = RCTSurfaceStageSurfaceDidInitialize;
   }
 
@@ -106,6 +104,7 @@ using namespace facebook::react;
 
   if (!_view) {
     _view = [[RCTSurfaceView alloc] initWithSurface:(RCTSurface *)self];
+    _touchHandler = [RCTSurfaceTouchHandler new];
     [_touchHandler attachToView:_view];
   }