Prepare View Transitions for launch as part of Performance Lab program

[felixarntz]

Summary

See #1997.

Pending merge of #2025.

[github-actions]

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Co-authored-by: felixarntz <[email protected]>
Co-authored-by: swissspidy <[email protected]>
Co-authored-by: ShyamGadde <[email protected]>
Co-authored-by: mukeshpanchal27 <[email protected]>
Co-authored-by: westonruter <[email protected]>

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 72.20%. Comparing base (79fd9c0) to head (c25ce29).
Report is 18 commits behind head on trunk.

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk    #2027      +/-   ##
==========================================
+ Coverage   70.01%   72.20%   +2.18%     
==========================================
  Files          91       90       -1     
  Lines        7603     7403     -200     
==========================================
+ Hits         5323     5345      +22     
+ Misses       2280     2058     -222     

Flag	Coverage Δ
multisite	72.20% <100.00%> (+2.18%)	⬆️
single	40.96% <100.00%> (+1.36%)	⬆️

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[westonruter]

FYI: Before we release the View Transitions plugin, there's some TypeScript issues that need to be addressed: #2029.

[felixarntz]

@westonruter I addressed the most critical part (missing property in the types) as part of #2025. I think the remainder can be separately addressed, as any of these are not causing any user-facing problems as far as I can tell.