test(lean/run): add notation test

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
refactor(frontends/lean/builtin_cmds): move declaration commands to new file

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): add inductive_cmd

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
feat(frontends/lean): add inductive_cmd