feat(library/elaborator): expose elaborator configuration options

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): position information in error messages

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean/pp): change how lift local entries are pretty printed

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