Change visibility of some build targets that are publicly used.

Bug: None
Change-Id: I9b0dc56364648ac4d4fa4b8bb67af44700621b24
Reviewed-on: https://webrtc-review.googlesource.com/93282
Reviewed-by: Anders Carlsson <andersc@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24256}

sdk/BUILD.gn

@@ -55,6 +55,7 @@ if (is_ios || is_mac) {
   }
 
   rtc_static_library("common_objc") {
+    visibility = [ "*" ]
     sources = [
       "objc/Framework/Classes/Common/NSString+StdString.h",
       "objc/Framework/Classes/Common/NSString+StdString.mm",
@@ -231,6 +232,7 @@ if (is_ios || is_mac) {
     }
 
     rtc_static_library("videoframebuffer_objc") {
+      visibility = [ "*" ]
       sources = [
         "objc/Framework/Classes/PeerConnection/RTCVideoFrame.mm",
         "objc/Framework/Classes/Video/RTCCVPixelBuffer.mm",