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/experiments/BUILD.gn

@@ -0,0 +1,26 @@
+# Copyright (c) 2022 The WebRTC project authors. All Rights Reserved.
+#
+# Use of this source code is governed by a BSD-style license
+# that can be found in the LICENSE file in the root of the source
+# tree. An additional intellectual property rights grant can be found
+# in the file PATENTS.  All contributing project authors may
+# be found in the AUTHORS file in the root of the source tree.
+
+import("../webrtc.gni")
+
+action("registered_field_trials_header") {
+  visibility = [ ":*" ]
+  script = "field_trials.py"
+  args = [
+    "header",
+    "--output",
+    rebase_path(target_gen_dir, root_build_dir) + "/registered_field_trials.h",
+  ]
+  outputs = [ "$target_gen_dir/registered_field_trials.h" ]
+}
+
+rtc_library("registered_field_trials") {
+  visibility = [ "*" ]
+  sources = get_target_outputs(":registered_field_trials_header")
+  deps = [ ":registered_field_trials_header" ]
+}