Refactor HashContext into an object.

This allows better type hinting as well as potentially adding
methods in a followup diff.

Original patch by Rouven Weßling (github.com/realityking)
Heavily modified by Sara Golemon (github.com/sgolemon)

Author: realityking

NEWS

@@ -75,6 +75,7 @@ PHP                                                                        NEWS
 - hash:
   . Fixed bug #73961 (environmental build dependency in hash sha3 source).
     (krakjoe)
+  . Changed HashContext from resource to object. (Rouven Weßling, Sara)
 
 - Mbstring:
   . Implemented request #66024 (mb_chr() and mb_ord()). (Masakielastic, Yasuo)