Fix the normalization of unshaped letters

- I updated it since I forget to update it when I moved from using
unsigned vectors to using string with utf8iterator to iterate them

- It should be done for all letters before applying other actions so I
moved it alone not with the "if else if" chain
use space-based indenation in arabic-normalizer-constants.h
instead of tab-based
Use the defined constants instead of literal value for Arabic letters
in shaping and buckwalter mappings