Remove stringstream fallback from MakeVal in logging.h

This change removes the generic MakeVal fallback in logging.h that
relied on std::ostringstream. This hasn't been used in webrtc for years
but now known downstream dependencies have been removed in favor of more
efficient alternatives like StringBuilder and Abseil's string utilities.

Existing call sites and related code in tests and tools have similarly
been migrated:

* Replaced std::ostringstream and std::stringstream with StringBuilder
  in SDP, Opus, and OpenSSL unit tests.
* Refactored string parsing in neteq_quality_test and bwe_rtp to use
  absl::StrSplit and Abseil's numeric conversion functions.
* Updated RTC_LOG calls in cross_traffic_unittest to explicitly load
  atomic counters (and not rely on stringstream to do it).
* Updated BUILD.gn and DEPS to include required Abseil and string
  utility dependencies.

Bug: webrtc:42234461
Change-Id: I7fbe4b68478fb1aca08c6126979ae577ef5418da
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/466441
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Reviewed-by: Jakob Ivarsson‎ <jakobi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#47577}