Add support for graphics redirection protocol

Add support for new graphics redirection protocol (aka VAIL) used by
WSLg. This protocol is currently being documented and the official
documentation will be posted in the near future.

channels/gfxredir/CMakeLists.txt

@@ -0,0 +1,23 @@
+# FreeRDP: A Remote Desktop Protocol Implementation
+# FreeRDP cmake build script
+#
+# Copyright 2020 Microsoft
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+if(WITH_CHANNEL_GFXREDIR)
+	define_channel("gfxredir")
+	if(WITH_SERVER_CHANNELS)
+		add_channel_server(${MODULE_PREFIX} ${CHANNEL_NAME})
+	endif()
+endif()