fix(kernel/type_checker): bug in quick_is_conv, it was not converting free variables to local constants.

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

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(kernel/max_sharing): add example exposing bug in max_sharing_fn, and fix it

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