Expose public method to find VC (#3339)

* Provide findViewController api method

* Fix merge changes

* Optional resizeMode

* Update Element typings

lib/ios/RNNBridgeManager.h

 #import <Foundation/Foundation.h>
 #import <React/RCTBridge.h>
 #import "RNNBridgeManagerDelegate.h"
+#import "RNNStore.h"
 
 typedef UIViewController * (^RNNExternalViewCreator)(NSDictionary* props, RCTBridge* bridge);
 
 - (void)registerExternalComponent:(NSString *)name callback:(RNNExternalViewCreator)callback;
 
 @property (readonly, nonatomic, strong) RCTBridge *bridge;
+@property (readonly, nonatomic, strong) RNNStore *store;
 
 @end

lib/ios/RNNBridgeManager.m

 @interface RNNBridgeManager() <RCTBridgeDelegate>
 
 @property (nonatomic, strong, readwrite) RCTBridge *bridge;
+@property (nonatomic, strong, readwrite) RNNStore *store;
 
 @end
 

lib/ios/ReactNativeNavigation.h

 
 + (void)registerExternalComponent:(NSString *)name callback:(RNNExternalViewCreator)callback;
 
++ (UIViewController *)findViewController:(NSString *)componentId;
+
 + (RCTBridge *)getBridge;
 
 @end

lib/ios/ReactNativeNavigation.m

 	return [[ReactNativeNavigation sharedInstance].bridgeManager bridge];
 }
 
++ (UIViewController *)findViewController:(NSString *)componentId {
+    RNNStore *store = [[ReactNativeNavigation sharedInstance].bridgeManager store];
+    return [store findComponentForId:componentId];
+}
 
 # pragma mark - instance
 

lib/src/Navigation.ts

 import { ComponentType } from 'react';
 
 export class Navigation {
-  public readonly Element: React.ComponentType<{ elementId: any; resizeMode: any; }>;
+  public readonly Element: React.ComponentType<{ elementId: any; resizeMode?: any; }>;
   public readonly store: Store;
   private readonly nativeEventsReceiver: NativeEventsReceiver;
   private readonly uniqueIdProvider: UniqueIdProvider;

lib/src/adapters/Element.tsx

 
 let RNNElement: React.ComponentType<any>;
 
-export class Element extends React.Component<{ elementId: any; resizeMode: any; }, any> {
+export class Element extends React.Component<{ elementId: any; resizeMode?: any; }, any> {
   static propTypes = {
     elementId: PropTypes.string.isRequired,
     resizeMode: PropTypes.string