[Docker] LLVM: allow placeholders/replacement in versions argument

[GuillaumeDua]

Allow placeholders/replacement in versions argument

And removes duplicates, for instance latest and latest-stable might be the same.

Example:

  ./.devcontainer/scripts/llvm.sh --versions="latest latest-stable" --list --silent=0

(as writing)

  --versions="19 18"

As well as:

  ./.devcontainer/scripts/llvm.sh --versions=">=17 latest latest-stable" --list --silent=0

  --versions="17 18 19"

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Then update the github-actions accordingly ?