Manage passes via `PassManager`
Once this is completed in LFortran, I will add it to LPython as well.
Covers all the features listed in https://github.com/lcompilers/lpython/issues/656. Now user can also apply only a selected list of passes before the code is passed on to the backends. Multiple passes can also be applied by specifying them in comma separated fashion.
Edited by Gagandeep Singh