Add missing Custom Native delegate, property to Native Add and rename Native Ad delegate.

[Flash3001]

Add missing GADCustomNativeAdLoaderDelegate;

/// The delegate of a GADAdLoader object implements this protocol to receive
/// GADCustomNativeAd ads.
@protocol GADCustomNativeAdLoaderDelegate <GADAdLoaderDelegate>

/// Called when requesting an ad. Asks the delegate for an array of custom native ad format ID
/// strings.
- (nonnull NSArray<NSString *> *)customNativeAdFormatIDsForAdLoader:(nonnull GADAdLoader *)adLoader;

/// Tells the delegate that a custom native ad was received.
- (void)adLoader:(nonnull GADAdLoader *)adLoader
    didReceiveCustomNativeAd:(nonnull GADCustomNativeAd *)customNativeAd;

@end

Rename GADUnifiedNativeAdLoaderDelegate to GADNativeAdLoaderDelegate;

/// The delegate of a GADAdLoader object implements this protocol to receive GADNativeAd ads.
@protocol GADNativeAdLoaderDelegate <GADAdLoaderDelegate>
/// Called when a native ad is received.
- (void)adLoader:(nonnull GADAdLoader *)adLoader didReceiveNativeAd:(nonnull GADNativeAd *)nativeAd;
@end

Add missing headline to NativeAd;

/// Headline.
@property(nonatomic, readonly, copy, nullable) NSString *headline;

[Flash3001]

@microsoft-github-policy-service agree