Make RTCAudioSession accessible to Swift.

This is done by:
1. removing the <vector> include from RTCAudioSession+Private,
2. creating a audio_session_objc package that excludes the RTCNativeAudioSessionDelegateAdapter class.

Bug: webrtc:11237
Change-Id: I36c86542a19e3244456fd164d908563b1435de29
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/163900
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Chuck Hays <haysc@webrtc.org>
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30177}

sdk/objc/components/audio/RTCAudioSession+Private.h

@@ -10,8 +10,6 @@
 
 #import "RTCAudioSession.h"
 
-#include <vector>
-
 NS_ASSUME_NONNULL_BEGIN
 
 @class RTCAudioSessionConfiguration;
@@ -77,8 +75,6 @@ NS_ASSUME_NONNULL_BEGIN
 - (NSError *)configurationErrorWithDescription:(NSString *)description;
 
 // Properties and methods for tests.
-@property(nonatomic, readonly) std::vector<__weak id<RTCAudioSessionDelegate> > delegates;
-
 - (void)notifyDidBeginInterruption;
 - (void)notifyDidEndInterruptionWithShouldResumeSession:(BOOL)shouldResumeSession;
 - (void)notifyDidChangeRouteWithReason:(AVAudioSessionRouteChangeReason)reason

sdk/objc/components/audio/RTCAudioSession.mm

@@ -12,6 +12,8 @@
 
 #import <UIKit/UIKit.h>
 
+#include <vector>
+
 #include "rtc_base/atomic_ops.h"
 #include "rtc_base/checks.h"
 #include "rtc_base/critical_section.h"
@@ -25,6 +27,10 @@ NSInteger const kRTCAudioSessionErrorLockRequired = -1;
 NSInteger const kRTCAudioSessionErrorConfiguration = -2;
 NSString * const kRTCAudioSessionOutputVolumeSelector = @"outputVolume";
 
+@interface RTCAudioSession ()
+@property(nonatomic, readonly) std::vector<__weak id<RTCAudioSessionDelegate> > delegates;
+@end
+
 // This class needs to be thread-safe because it is accessed from many threads.
 // TODO(tkchin): Consider more granular locking. We're not expecting a lot of
 // lock contention so coarse locks should be fine for now.