Fix RCTAlertController import when embed in existing iOS projects (#32457)

Summary:
Fixes a build error relating to RCTAlertController import when embedding react-native into existing iOS app. This PR resolves the issue detailed in #32356

## Changelog

Adjusts the import syntax which was added in:
f319ff3#diff-56beca6ee071cdd162c269ce765ab12d5af8c8c0ca840bca1e9d1f59e9fab790

Existing:
#import "RCTAlertController.h"

New:
#import <React/RCTAlertController.h>

[iOS] [Fix] - Fix RCTAlertController import build error when embedded in existing iOS projects

Pull Request resolved: #32457

Test Plan:
Build this branch in existing iOS project using swift, and should not have the build error described in the issue above.

Would also like to have this fix cherry-pick'd to release 0.63 after merging.

Reviewed By: RSNara

Differential Revision: D31861814

Pulled By: charlesbdudley

fbshipit-source-id: e60f80c8ea982e400cbf6d9375037d4197bbb8a3

Author: nickfujita

React/CoreModules/RCTAlertController.m

@@ -7,7 +7,7 @@
 
 #import <React/RCTUtils.h>
 
-#import "RCTAlertController.h"
+#import <React/RCTAlertController.h>
 
 @interface RCTAlertController ()