refactor(frontends/lean/info_manager): intrusive smart pointer for info_data

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(frontends/lean/info_manager): to allow cache to be used when producing info data, fixes #37, closes #45

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(frontends/lean/info_manager): to allow cache to be used when producing info data, fixes #37, closes #45