devcontainer: expose host config, fix mac screen issues (#29932)

* export host config via .host/.env file. fix mac display issues

* append instead of replace for bashrc

* Log when mac display override happens

* Update xauthority path in json

.devcontainer/container_post_create.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+source .devcontainer/.host/.env
+
+# override display flag for mac
+if [[ $HOST_OS == darwin ]]; then
+  echo "Setting up DISPLAY override for macOS..."
+  cat <<EOF >> /root/.bashrc
+if [ -n "\$DISPLAY" ]; then
+  DISPLAY_NUM=\$(echo "\$DISPLAY" | awk -F: '{print \$NF}')
+  export DISPLAY=host.docker.internal:\$DISPLAY_NUM
+fi
+EOF
+fi