Handle isalpha and istitle like isupper, islower and several `is*` checks 

recently I encountered type mismatch error in one of my PRs https://github.com/lcompilers/lpython/pull/2357 and then I realised that that I had handled  `isalpha and istitle` differently then it should be handled , I will handle it just like i did for `isspace` in one of my PR.