Use code shim instead of alias (#575)

script-library/common-debian.sh

@@ -183,13 +183,30 @@ RC_SNIPPET="$(cat << EOF
 export USER=\$(whoami)
 
 export PATH=\$PATH:\$HOME/.local/bin
-
-if type code-insiders > /dev/null 2>&1 && ! type code > /dev/null 2>&1; then 
-    alias code=code-insiders
-fi
 EOF
 )"
 
+# code shim, it fallbacks to code-insiders if code is not available
+cat << 'EOF' > /usr/local/bin/code
+#!/bin/sh
+
+get_in_path_except_current() {
+  which -a "$1" | grep -v "$0" | head -1
+}
+
+code="$(get_in_path_except_current code)"
+
+if [ -n "$code" ]; then
+  exec "$code" "$@"
+elif [ "$(command -v code-insiders)" ]; then
+  exec code-insiders "$@"
+else
+  echo "code or code-insiders is not installed" >&2
+  exit 127
+fi
+EOF
+chmod +x /usr/local/bin/code
+
 # Codespaces themes - partly inspired by https://github.com/ohmyzsh/ohmyzsh/blob/master/themes/robbyrussell.zsh-theme
 CODESPACES_BASH="$(cat \
 <<EOF