[NO-ISSUE] WIP use eclair-lang to replace Soufflé Datalog

[tchoutri]

This is a minimal, non-intrusive WIP to replace soufflé by éclair.

One final major step before the adoption is possible is that éclair is bootstrappable and doesn't need the soufflé semantic analysis file at runtime.

cc @luc-tielen

[tchoutri]

@mergifyIO rebase

[mergify[bot]]

rebase

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