Add missing Foundation imports to Interop headers (#2207)

Author: paulb777

Interop/Analytics/Public/FIRInteropEventNames.h

@@ -16,6 +16,8 @@
 
 /// @file FIRInteropEventNames.h
 
+#import <Foundation/Foundation.h>
+
 /// Notification open event name.
 static NSString *const kFIRIEventNotificationOpen = @"_no";
 

Interop/Analytics/Public/FIRInteropParameterNames.h

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#import <Foundation/Foundation.h>
+
 /// @file FIRInteropParameterNames.h
 ///
 /// Predefined event parameter names used by Firebase. This file is a subset of the

Interop/Auth/Public/FIRAuthInterop.h

@@ -17,6 +17,8 @@
 #ifndef FIRAuthInterop_h
 #define FIRAuthInterop_h
 
+#import <Foundation/Foundation.h>
+
 NS_ASSUME_NONNULL_BEGIN
 
 /** @typedef FIRTokenCallback