Omit admin View Transitions functionality when present in core

[westonruter]

See WordPress/wordpress-develop#10699

Without 7.0-alpha	With 7.0-alpha

[github-actions]

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Co-authored-by: westonruter <westonruter@git.wordpress.org>
Co-authored-by: felixarntz <flixos90@git.wordpress.org>
Co-authored-by: mukeshpanchal27 <mukesh27@git.wordpress.org>

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.19%. Comparing base (c9720dc) to head (5a65d35).
⚠️ Report is 10 commits behind head on trunk.

Files with missing lines	Patch %	Lines
plugins/view-transitions/includes/settings.php	0.00%	16 Missing ⚠️
plugins/view-transitions/includes/admin.php	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk    #2344      +/-   ##
==========================================
- Coverage   69.21%   69.19%   -0.03%     
==========================================
  Files          90       90              
  Lines        7703     7706       +3     
==========================================
  Hits         5332     5332              
- Misses       2371     2374       +3     

Flag	Coverage Δ
multisite	69.19% <0.00%> (-0.03%)	⬇️
single	35.40% <0.00%> (-0.02%)	⬇️

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[felixarntz]

@westonruter Thanks!