add while to matchless

[johnynek]

this closes #770 by moving a lot of the logic of while construction into a single place, then generate while loops after. This unifies 3 implementations (MatchlessToValue, python, c).

It also opens the door to possibly remove the SearchList node since I think that can be rewritten as a while loop.

[codecov]

Codecov Report

Attention: Patch coverage is 94.64286% with 9 lines in your changes missing coverage. Please review.

Project coverage is 89.34%. Comparing base (04a0e87) to head (0db54bc).
Report is 110 commits behind head on main.

Files with missing lines	Patch %	Lines
...main/scala/org/bykn/bosatsu/MatchlessToValue.scala	89.58%	5 Missing ⚠️
...re/src/main/scala/org/bykn/bosatsu/Matchless.scala	95.83%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1299      +/-   ##
==========================================
- Coverage   91.32%   89.34%   -1.98%     
==========================================
  Files          96      106      +10     
  Lines       11846    13335    +1489     
  Branches     2675     3054     +379     
==========================================
+ Hits        10818    11914    +1096     
- Misses       1028     1421     +393     

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