Add shell completion for homebrew installation

[near129]

This pull request aims to enable automatic shell completion during the Homebrew installation process, similar to this reference. To achieve this, the pull request includes changes to incorporate shell completion scripts within the WezTerm.app.

related: wez/homebrew-wezterm#7

Note:
Upon successful merging and release of this pull request, it will be necessary to add the following code to the Homebrew Formula:

  binary "WezTerm.app/Contents/Resources/shell-completion/zsh",
         target: "#{HOMEBREW_PREFIX}/share/zsh/site-functions/_wezterm"
  binary "WezTerm.app/Contents/Resources/shell-completion/bash",
         target: "#{HOMEBREW_PREFIX}/etc/bash_completion.d/wezterm"
  binary "WezTerm.app/Contents/Resources/shell-completion/fish",
         target: "#{HOMEBREW_PREFIX}/share/fish/vendor_completions.d/wezterm.fish"

[wez]

Thanks!
Will you also submit PR(s) for the homebrew specific portions?

[near129]

OK. I have submitted it to wez/homebrew-wezterm#11.
Please note that this PR has not been released yet, so it cannot be merged.