[FEATURE] Generalize prec_to_type and type_to_prec dictionary

[Siddhartha Dhar Choudhury]

Describe the solution you'd like
Two dictionaries called prec_to_type and type_to_prec have been created multiple times in the parser, these map an integer precedence to typename and typename to precedence integer respectively. If there is requirement of adding a new typename with precedence in between these values then one will have to change all these dictionaries. It would thus be better to have a single dictionary in parser_constants.py which can be used everywhere.