feat(frontends/lean): add '#setline' directive

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(shell/lean): add '-o' command line option

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(frontends/lean): add local_decls template that is cheap to copy

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): add command block reader with snapshot and resume

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