Implement KnownLayout for f16 and f128

[usamoi]

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.46%. Comparing base (f495088) to head (9013978).

Additional details and impacted files

@@            Coverage Diff             @@
##           v0.8.x    #2250      +/-   ##
==========================================
+ Coverage   87.42%   87.46%   +0.03%     
==========================================
  Files          16       16              
  Lines        6115     6134      +19     
==========================================
+ Hits         5346     5365      +19     
  Misses        769      769              

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