Remove simple stringstream usages.

This CL replaces std::o?stringstream with rtc::StringBuilder where that's possible to do without changing any of the surrounding code. It also updates includes and build files as appropriate.

The CL was generated by running 'git grep -l -P std::o?stringstream | xargs perl -pi -e "s/std::o?stringstream/rtc::StringBuilder/g"'. Then I've manually updated the #includes and BUILD files, run 'git cl format' and unstaged any file that would need more complex fixes.

Bug: webrtc:8982
Change-Id: Ibc32153f4a3fd177e260b6ad05ce393972549357
Reviewed-on: https://webrtc-review.googlesource.com/98460
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Jonas Olsson <jonasolsson@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24605}
diff --git a/api/BUILD.gn b/api/BUILD.gn
index f8b6ca3..b6ad1d6 100644
--- a/api/BUILD.gn
+++ b/api/BUILD.gn
@@ -387,6 +387,7 @@
     deps = [
       "..:webrtc_common",
       "../modules/video_coding:video_codec_interface",
+      "../rtc_base:stringutils",
       "video_codecs:video_codecs_api",
     ]
   }