PF Diff tests for secrets

[VenelinMartinov]

This change adds tests for PF handling of secrets in previews.

This covers:

• secret attributes
• secrets elements in set attributes,
• secret collection attributes
• secrets properties in blocks
• secret blocks
• secrets coming from pulumi schema

[VenelinMartinov]

This change is part of the following stack:

• PF Diff cross-tests for sets with defaults #2640
  • PF Diff tests for secrets #2642 ◀
    • Fix PF provider_server detailed diff handling #2628
      • PF detailed diff #2629
        • Detailed diff handle secrets and outputs #2643

_{Change managed by git-spice.}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.97%. Comparing base (bef446f) to head (ad7f844).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2642   +/-   ##
=======================================
  Coverage   69.97%   69.97%           
=======================================
  Files         367      367           
  Lines       44503    44503           
=======================================
+ Hits        31140    31141    +1     
- Misses      11734    11735    +1     
+ Partials     1629     1627    -2     

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[pulumi-bot]

This PR has been shipped in release v3.96.0.