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/util/python/BUILD.bazel

@@ -0,0 +1,22 @@
+load("@rules_cc//cc:defs.bzl", "cc_library")
+
+exports_files(["BUILD.bazel"])
+
+# This is a placeholder for python headers. Projects needing to use
+# fast cpp protos in protobuf's python interface should build with
+# --define=use_fast_cpp_protos=true, and in addition, provide
+# //external:python_headers dependency that in turn provides Python.h.
+#
+# Projects that include protobuf using a Bazel external repository will need to
+# add a workspace rule to their WORKSPACE files to add an external workspace
+# that includes the Python headers. For example, the protobuf WORKSPACE file
+# includes the following local_repository rule that points to this directory:
+#
+# new_local_repository(
+#   name = "python_headers",
+#   path = __workspace_dir__ + "/util/python",
+# )
+cc_library(
+    name = "python_headers",
+    visibility = ["//visibility:public"],
+)