feat(collections/unstable): add "union" to DeepMergeOptions.arrays

[DonBLong]

Adds a "union" MergingStrategy for arrays only, through a new exported type ArraysMergingStrategy. Implementation uses the union function imported from "./union.ts"

closes: #7048

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.39%. Comparing base (260f5b8) to head (d30e9e7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7049      +/-   ##
==========================================
+ Coverage   94.38%   94.39%   +0.01%     
==========================================
  Files         628      629       +1     
  Lines       50175    50286     +111     
  Branches     8840     8868      +28     
==========================================
+ Hits        47357    47468     +111     
  Misses       2251     2251              
  Partials      567      567              

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