Add reset method to RCTFabricSurface [2/N]

Summary:
This method allows a surface to re-render from scratch, without having to delete and reinstantiate the surface.

Changelog: [iOS] Added reset method to RCTFabricSurface to help with reloads

Reviewed By: RSNara

Differential Revision: D25000509

fbshipit-source-id: f74170aa78cc84491ad2679f130ed3c8965bbe34

React/Fabric/Surface/RCTFabricSurface.h

@@ -70,6 +70,13 @@ NS_ASSUME_NONNULL_BEGIN
 - (BOOL)start;
 - (BOOL)stop;
 
+/**
+ * EXPERIMENTAL
+ * Reset's the Surface to it's initial stage.
+ * It uses the passed in surface presenter, and whatever else was passed in init.
+ */
+- (void)resetWithSurfacePresenter:(RCTSurfacePresenter *)surfacePresenter;
+
 #pragma mark - Layout: Setting the size constrains
 
 /**

React/Fabric/Surface/RCTFabricSurface.mm

@@ -64,6 +64,13 @@ - (instancetype)initWithSurfacePresenter:(RCTSurfacePresenter *)surfacePresenter
   return self;
 }
 
+- (void)resetWithSurfacePresenter:(RCTSurfacePresenter *)surfacePresenter
+{
+  _surfacePresenter = surfacePresenter;
+  _stage = RCTSurfaceStageSurfaceDidInitialize;
+  _view = nil;
+}
+
 - (BOOL)start
 {
   if (![self _setStage:RCTSurfaceStageStarted]) {