Wrap WebRTC OBJC API types with RTC_OBJC_TYPE.

This CL introduced 2 new macros that affect the WebRTC OBJC API symbols:

- RTC_OBJC_TYPE_PREFIX:
  Macro used to prepend a prefix to the API types that are exported with
  RTC_OBJC_EXPORT.

  Clients can patch the definition of this macro locally and build
  WebRTC.framework with their own prefix in case symbol clashing is a
  problem.

  This macro must only be defined by changing the value in
  sdk/objc/base/RTCMacros.h  and not on via compiler flag to ensure
  it has a unique value.

- RCT_OBJC_TYPE:
  Macro used internally to reference API types. Declaring an API type
  without using this macro will not include the declared type in the
  set of types that will be affected by the configurable
  RTC_OBJC_TYPE_PREFIX.

Manual changes:
https://webrtc-review.googlesource.com/c/src/+/173781/5..10

The auto-generated changes in PS#5 have been done with:
https://webrtc-review.googlesource.com/c/src/+/174061.

Bug: None
Change-Id: I0d54ca94db764fb3b6cb4365873f79e14cd879b8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/173781
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Kári Helgason <kthelgason@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31153}

sdk/objc/components/video_codec/RTCDefaultVideoDecoderFactory.m

@@ -19,31 +19,33 @@
 #import "api/video_codec/RTCVideoDecoderVP9.h"
 #endif
 
-@implementation RTCDefaultVideoDecoderFactory
+@implementation RTC_OBJC_TYPE (RTCDefaultVideoDecoderFactory)
 
-- (NSArray<RTCVideoCodecInfo *> *)supportedCodecs {
+- (NSArray<RTC_OBJC_TYPE(RTCVideoCodecInfo) *> *)supportedCodecs {
   NSDictionary<NSString *, NSString *> *constrainedHighParams = @{
     @"profile-level-id" : kRTCMaxSupportedH264ProfileLevelConstrainedHigh,
     @"level-asymmetry-allowed" : @"1",
     @"packetization-mode" : @"1",
   };
-  RTCVideoCodecInfo *constrainedHighInfo =
-      [[RTCVideoCodecInfo alloc] initWithName:kRTCVideoCodecH264Name
-                                   parameters:constrainedHighParams];
+  RTC_OBJC_TYPE(RTCVideoCodecInfo) *constrainedHighInfo =
+      [[RTC_OBJC_TYPE(RTCVideoCodecInfo) alloc] initWithName:kRTCVideoCodecH264Name
+                                                  parameters:constrainedHighParams];
 
   NSDictionary<NSString *, NSString *> *constrainedBaselineParams = @{
     @"profile-level-id" : kRTCMaxSupportedH264ProfileLevelConstrainedBaseline,
     @"level-asymmetry-allowed" : @"1",
     @"packetization-mode" : @"1",
   };
-  RTCVideoCodecInfo *constrainedBaselineInfo =
-      [[RTCVideoCodecInfo alloc] initWithName:kRTCVideoCodecH264Name
-                                   parameters:constrainedBaselineParams];
+  RTC_OBJC_TYPE(RTCVideoCodecInfo) *constrainedBaselineInfo =
+      [[RTC_OBJC_TYPE(RTCVideoCodecInfo) alloc] initWithName:kRTCVideoCodecH264Name
+                                                  parameters:constrainedBaselineParams];
 
-  RTCVideoCodecInfo *vp8Info = [[RTCVideoCodecInfo alloc] initWithName:kRTCVideoCodecVp8Name];
+  RTC_OBJC_TYPE(RTCVideoCodecInfo) *vp8Info =
+      [[RTC_OBJC_TYPE(RTCVideoCodecInfo) alloc] initWithName:kRTCVideoCodecVp8Name];
 
 #if defined(RTC_ENABLE_VP9)
-  RTCVideoCodecInfo *vp9Info = [[RTCVideoCodecInfo alloc] initWithName:kRTCVideoCodecVp9Name];
+  RTC_OBJC_TYPE(RTCVideoCodecInfo) *vp9Info =
+      [[RTC_OBJC_TYPE(RTCVideoCodecInfo) alloc] initWithName:kRTCVideoCodecVp9Name];
 #endif
 
   return @[
@@ -56,14 +58,14 @@
   ];
 }
 
-- (id<RTCVideoDecoder>)createDecoder:(RTCVideoCodecInfo *)info {
+- (id<RTC_OBJC_TYPE(RTCVideoDecoder)>)createDecoder:(RTC_OBJC_TYPE(RTCVideoCodecInfo) *)info {
   if ([info.name isEqualToString:kRTCVideoCodecH264Name]) {
-    return [[RTCVideoDecoderH264 alloc] init];
+    return [[RTC_OBJC_TYPE(RTCVideoDecoderH264) alloc] init];
   } else if ([info.name isEqualToString:kRTCVideoCodecVp8Name]) {
-    return [RTCVideoDecoderVP8 vp8Decoder];
+    return [RTC_OBJC_TYPE(RTCVideoDecoderVP8) vp8Decoder];
 #if defined(RTC_ENABLE_VP9)
   } else if ([info.name isEqualToString:kRTCVideoCodecVp9Name]) {
-    return [RTCVideoDecoderVP9 vp9Decoder];
+    return [RTC_OBJC_TYPE(RTCVideoDecoderVP9) vp9Decoder];
 #endif
   }