rename host preload -> start (#37422)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/37422

Changelog: [Internal]

in this simple change, i renamed the `preload` API, which triggers all the rct instance / javascript runtime creation to `start`. `preload` is a confusing API on the host because the host should be agnostic of when the timing to create its dependencies are, and the consumer should determine when initialization is lazy, early, etc.

Reviewed By: cipolleschi

Differential Revision: D45760583

fbshipit-source-id: bea26d21f950474352280292426a5facbe52b60f

packages/react-native/ReactCommon/react/bridgeless/platform/ios/Core/RCTHost.h

@@ -67,7 +67,7 @@ typedef std::shared_ptr<facebook::react::JSEngineInstance> (^RCTHostJSEngineProv
  * main thread, but it should be threadsafe.
  * TODO T74233481 - Verify if this function is threadsafe.
  */
-- (void)preload;
+- (void)start;
 
 - (RCTFabricSurface *)createSurfaceWithModuleName:(NSString *)moduleName
                                              mode:(facebook::react::DisplayMode)displayMode

packages/react-native/ReactCommon/react/bridgeless/platform/ios/Core/RCTHost.mm

@@ -140,7 +140,7 @@ NSString *const RCTHostDidReloadNotification = @"RCTHostDidReloadNotification";
 
 #pragma mark - Public
 
-- (void)preload
+- (void)start
 {
   if (_instance) {
     RCTLogWarn(