Split runtime utilities out of stake_state.rs

[CriesofCarrots]

Problem

solana_stake_program::stake_state is a bit of a kitchen sink; it is difficult to distinguish which parts are critical to the runtime, and which are critical to the existing program processor.

Summary of Changes

Split out the runtime utilities:

• Split fn calculate_points() and dependencies into a new points module
• Split fn redeem_rewards() and dependencies into a new rewards module. This is hidden from docs since the only public fn is also hidden.

No functional changes. Only moving code.

[codecov]

Codecov Report

Attention: Patch coverage is 90.93851% with 28 lines in your changes are missing coverage. Please review.

Project coverage is 81.7%. Comparing base (e8c87e8) to head (fc0f76f).

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #35386     +/-   ##
=========================================
- Coverage    81.8%    81.7%   -0.1%     
=========================================
  Files         834      836      +2     
  Lines      224815   224821      +6     
=========================================
- Hits       183919   183855     -64     
- Misses      40896    40966     +70     

[joncinque]

Looks good to me! Note that I didn't examine everything super closely, I mainly looked at the functions and test names that were moved