test(tests/lean): new error msg test

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(library/elaborator): bug in process_lower

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(tests/lean): add example that cannot be elaborated

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(kernel/normalizer): metavariable reification

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(library/elaborator): bug in free variable normalization (lift was missing)

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
test(tests/lean): add new normalizer/elaborator test

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>