Bump to WebRTC M131 release

Ongoing fixes and improvements, transient suppressor is gone. Also,
dropping isac because it doesn't seem to be useful, and is just build
system deadweight now.

Upstream references:

  Version: 131.0.6778.200
  WebRTC: 79aff54b0fa9238ce3518dd9eaf9610cd6f22e82
  Chromium: 2a19506ad24af755f2a215a4c61f775393e0db42

webrtc/api/video/color_space.cc

@@ -10,6 +10,12 @@
 
 #include "api/video/color_space.h"
 
+#include <cstddef>
+#include <cstdint>
+#include <optional>
+#include <string>
+
+#include "api/video/hdr_metadata.h"
 #include "rtc_base/strings/string_builder.h"
 
 namespace webrtc {
@@ -95,8 +101,8 @@ ColorSpace::ColorSpace(PrimaryID primaries,
       range_(range),
       chroma_siting_horizontal_(chroma_siting_horz),
       chroma_siting_vertical_(chroma_siting_vert),
-      hdr_metadata_(hdr_metadata ? absl::make_optional(*hdr_metadata)
-                                 : absl::nullopt) {}
+      hdr_metadata_(hdr_metadata ? std::make_optional(*hdr_metadata)
+                                 : std::nullopt) {}
 
 ColorSpace::PrimaryID ColorSpace::primaries() const {
   return primaries_;
@@ -257,7 +263,7 @@ bool ColorSpace::set_chroma_siting_vertical_from_uint8(uint8_t enum_value) {
 
 void ColorSpace::set_hdr_metadata(const HdrMetadata* hdr_metadata) {
   hdr_metadata_ =
-      hdr_metadata ? absl::make_optional(*hdr_metadata) : absl::nullopt;
+      hdr_metadata ? std::make_optional(*hdr_metadata) : std::nullopt;
 }
 
 }  // namespace webrtc

webrtc/api/video/color_space.h

@@ -13,9 +13,9 @@
 
 #include <stdint.h>
 
+#include <optional>
 #include <string>
 
-#include "absl/types/optional.h"
 #include "api/video/hdr_metadata.h"
 #include "rtc_base/system/rtc_export.h"
 
@@ -174,7 +174,7 @@ class RTC_EXPORT ColorSpace {
   RangeID range_ = RangeID::kInvalid;
   ChromaSiting chroma_siting_horizontal_ = ChromaSiting::kUnspecified;
   ChromaSiting chroma_siting_vertical_ = ChromaSiting::kUnspecified;
-  absl::optional<HdrMetadata> hdr_metadata_;
+  std::optional<HdrMetadata> hdr_metadata_;
 };
 
 }  // namespace webrtc

webrtc/api/video/video_content_type.cc

@@ -10,6 +10,8 @@
 
 #include "api/video/video_content_type.h"
 
+#include <cstdint>
+
 #include "rtc_base/checks.h"
 
 namespace webrtc {

webrtc/api/video/video_timing.cc

@@ -11,6 +11,8 @@
 #include "api/video/video_timing.h"
 
 #include <algorithm>
+#include <cstdint>
+#include <string>
 
 #include "api/array_view.h"
 #include "api/units/time_delta.h"