Add FlStandardMessageCodec (#18213)

Author: robert-ancell

ci/licenses_golden/licenses_flutter

@@ -1199,6 +1199,9 @@ FILE: ../../../flutter/shell/platform/linux/fl_renderer.cc
 FILE: ../../../flutter/shell/platform/linux/fl_renderer.h
 FILE: ../../../flutter/shell/platform/linux/fl_renderer_x11.cc
 FILE: ../../../flutter/shell/platform/linux/fl_renderer_x11.h
+FILE: ../../../flutter/shell/platform/linux/fl_standard_message_codec.cc
+FILE: ../../../flutter/shell/platform/linux/fl_standard_message_codec_private.h
+FILE: ../../../flutter/shell/platform/linux/fl_standard_message_codec_test.cc
 FILE: ../../../flutter/shell/platform/linux/fl_string_codec.cc
 FILE: ../../../flutter/shell/platform/linux/fl_string_codec_test.cc
 FILE: ../../../flutter/shell/platform/linux/fl_value.cc
@@ -1209,6 +1212,7 @@ FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_binary_messe
 FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_dart_project.h
 FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_engine.h
 FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_message_codec.h
+FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_standard_message_codec.h
 FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_string_codec.h
 FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_value.h
 FILE: ../../../flutter/shell/platform/linux/public/flutter_linux/fl_view.h

shell/platform/linux/BUILD.gn

@@ -49,6 +49,7 @@ _public_headers = [
   "public/flutter_linux/fl_dart_project.h",
   "public/flutter_linux/fl_engine.h",
   "public/flutter_linux/fl_message_codec.h",
+  "public/flutter_linux/fl_standard_message_codec.h",
   "public/flutter_linux/fl_string_codec.h",
   "public/flutter_linux/fl_value.h",
   "public/flutter_linux/fl_view.h",
@@ -70,6 +71,7 @@ source_set("flutter_linux") {
     "fl_message_codec.cc",
     "fl_renderer.cc",
     "fl_renderer_x11.cc",
+    "fl_standard_message_codec.cc",
     "fl_string_codec.cc",
     "fl_value.cc",
     "fl_view.cc",
@@ -100,6 +102,7 @@ executable("flutter_linux_unittests") {
     "fl_binary_codec_test.cc",
     "fl_dart_project_test.cc",
     "fl_message_codec_test.cc",
+    "fl_standard_message_codec_test.cc",
     "fl_string_codec_test.cc",
     "fl_value_test.cc",
     "testing/fl_test.cc",