Diff cross tests for provider upgrades

[VenelinMartinov]

This PR adds a DiffProviderUpgradedSchema option to Diff cross-tests which allows us to test transitions between two different resource schemas.

It uses the same pulumitest mechanism (t.Run) as the upgrade tests.

I've also added a repro for #1667

Part of #2914

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.75%. Comparing base (55d6d45) to head (dc3f267).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2910   +/-   ##
=======================================
  Coverage   67.74%   67.75%           
=======================================
  Files         331      331           
  Lines       42210    42210           
=======================================
+ Hits        28596    28599    +3     
+ Misses      12019    12017    -2     
+ Partials     1595     1594    -1     

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[VenelinMartinov]

This change is part of the following stack:

• Diff cross tests for provider upgrades #2910 ◀
  • Add skip diff equivalence flag for Diff cross-tests #2913
    • Vvm/fix set elem conversion #2919
      • repro for maxItemsOne transitions #2912
  • restore internal-only PRC flag #2925

_{Change managed by git-spice.}