Rust engine: errors resugaring.

[maximebuyse]

The Error nodes in patterns, type, expression, etc. should be converted into “fake” patterns, “fake” types and “fake” expressions.

E.g., ExprKind::Error(err) should be translated in the application hax_error(formatted err)

[W95Psp]

Let's keep this PR alive: we will use it and merge it as soon as the Rust engine itself produces errros.