Add unit tests directly verifying individual building blocks of hash group by:

• hash calculation
• bit utilities introduced by hash group by
• comparison
• hash table core
• encoding and decoding of column-oriented data to row-oriented format

Reporter: Michal Nowakiewicz / @michalursa

Related issues:

• [C++] Query engine umbrella issue (is a child of)

_{Note: This issue was originally created as ARROW-12723. Please see the migration documentation for further details.}