Update Protobuf and add protos for CS2 (#176)

* Replace protobuf 2.6.1 with 3.21.8

* Update/add protobuf libs

* Add CS2 protos

* Remove old csgo/dota protos

* Add versioned protoc bin

* Comment out Valve's `schema` define for now

* Use ENetworkDisconnectionReason

* Fix-up `offsetof` to avoid errors on some Clang versions

thirdparty/protobuf-3.21.8/kokoro/linux/python38_cpp/build.sh

@@ -0,0 +1,18 @@
+#!/bin/bash
+#
+# This is the top-level script we give to Kokoro as the entry point for
+# running the "pull request" project:
+#
+# This script selects a specific Dockerfile (for building a Docker image) and
+# a script to run inside that image.  Then we delegate to the general
+# build_and_run_docker.sh script.
+
+# Change to repo root
+cd $(dirname $0)/../../..
+
+export DOCKERHUB_ORGANIZATION=protobuftesting
+export DOCKERFILE_DIR=kokoro/linux/dockerfile/test/python38
+export DOCKER_RUN_SCRIPT=kokoro/linux/pull_request_in_docker.sh
+export OUTPUT_DIR=testoutput
+export TEST_SET="python38_cpp"
+./kokoro/linux/build_and_run_docker.sh

thirdparty/protobuf-3.21.8/kokoro/linux/python38_cpp/continuous.cfg

@@ -0,0 +1,11 @@
+# Config file for running tests in Kokoro
+
+# Location of the build script in repository
+build_file: "protobuf/kokoro/linux/python38_cpp/build.sh"
+timeout_mins: 120
+
+action {
+  define_artifacts {
+    regex: "**/sponge_log.xml"
+  }
+}

thirdparty/protobuf-3.21.8/kokoro/linux/python38_cpp/presubmit.cfg

@@ -0,0 +1,11 @@
+# Config file for running tests in Kokoro
+
+# Location of the build script in repository
+build_file: "protobuf/kokoro/linux/python38_cpp/build.sh"
+timeout_mins: 120
+
+action {
+  define_artifacts {
+    regex: "**/sponge_log.xml"
+  }
+}