feat(arduino-cli): add completion plugin (#12522)

plugins/arduino-cli/README.md

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+# Arduino CLI plugin
+
+This plugin adds completion for the [arduino-cli](https://github.com/arduino/arduino-cli) tool.
+To use it, add `arduino-cli` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... arduino-cli)
+```

plugins/arduino-cli/arduino-cli.plugin.zsh

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+if (( ! $+commands[arduino-cli] )); then
+  return
+fi
+
+# If the completion file doesn't exist yet, we need to autoload it and
+# bind it to `arduino-cli`. Otherwise, compinit will have already done that.
+if [[ ! -f "$ZSH_CACHE_DIR/completions/_arduino-cli" ]]; then
+  typeset -g -A _comps
+  autoload -Uz _arduino-cli
+  _comps[arduino-cli]=_arduino-cli
+fi
+
+# Generate and load arduino-cli completion
+arduino-cli completion zsh >! "$ZSH_CACHE_DIR/completions/_arduino-cli" &|