Open visibility of some PC level framework components

Bug: webrtc:11479
Change-Id: I10567f2766e30825b4d28133002e04dcd0afba21
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/173901
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31129}

test/pc/e2e/BUILD.gn

@@ -455,6 +455,7 @@ if (rtc_include_tests) {
   }
 
   rtc_library("stats_poller") {
+    visibility = [ "*" ]
     testonly = true
     sources = [
       "stats_poller.cc",
@@ -599,6 +600,7 @@ rtc_library("network_quality_metrics_reporter") {
 }
 
 rtc_library("sdp_changer") {
+  visibility = [ "*" ]
   testonly = true
   sources = [
     "sdp/sdp_changer.cc",