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 94.03%. Comparing base (6df7f21) to head (8fde6b3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7049      +/-   ##
==========================================
+ Coverage   94.01%   94.03%   +0.01%     
==========================================
  Files         627      628       +1     
  Lines       50029    50140     +111     
  Branches     8807     8835      +28     
==========================================
+ Hits        47037    47148     +111     
  Misses       2413     2413              
  Partials      579      579              

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