Update visibility on rtc_base:log_sinks target

Some of the new targets are otherwise not visible by external users.

Bug: webrtc:9838
Change-Id: I7b92803692de64e0f93c9ec582c9fe615fda5e65
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/290844
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Auto-Submit: Florent Castelli <orphis@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#39068}

rtc_base/BUILD.gn

@@ -1320,6 +1320,7 @@ if (is_win) {
 
 if (!build_with_chromium) {
   rtc_library("log_sinks") {
+    visibility = [ "*" ]
     sources = [
       "log_sinks.cc",
       "log_sinks.h",