feat(bash_completion): Append user-defined aliases (if any) to the list of commands

[yermulnik]

Please refer to #22352 for details

Complement Bash Shell completion for top-level brew commands with user-defined aliases.

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[Copilot]

Pull request overview

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This PR updates Homebrew’s Bash completion to include user-defined brew aliases in the command completion list.

Changes:

• Adds an array to collect user-defined aliases and appends them to the commands list in __brew_complete_commands.
• Adds inline comments referencing the motivating PR for the alias behavior.

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[yermulnik]

Declined in favour of #22693