fix(frontends/lean): remove duplicate info entries, fix bug in save_overload

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): provide 'partial' type information even when there are type errors

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(frontends/lean): make sure typing information is sorted, make sure the error messages contains line file name

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
doc(server): describe server mode format

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