Improve shell completion

[Meakk]

Describe the bug Currently, shell completion (zsh, fish...) files are generated from f3d --help text and some hacky command to automatically format the completion files.

Expected behavior Instead, we should format the CLI options in a JSON files and parse the file in order to generate options for cxxopts.
That way, we could easily parse them into the completion files too.

System Information:

• OS: Linux

F3D Information 3.1

Bounty

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[debaa98]

Is there any specific bounty amount?

[mwestphal]

Hi @debaa98 . Bounty are reserved for returning contributors as documented here: https://f3d.app/doc/dev/GOVERNANCE.html#12-returning-contributors