refactor(testing): do not use assertEquals() in snapshot.ts

[kt3k]

Dependency to assertEquals from testing/snapshot was introduced in #3563 to avoid using non public API of assert from testing (That was necessary for a part of JSR migration).

Now those internal APIs diff, diffStr, and buildMessage are available from std/internal. This PR (partially) reverts #3563 and make testing/snapshot directly use those APIs from std/internal.

This unblocks #4893

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.12%. Comparing base (388800f) to head (a9c712c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4930      +/-   ##
==========================================
- Coverage   92.12%   92.12%   -0.01%     
==========================================
  Files         487      487              
  Lines       38772    38763       -9     
  Branches     5388     5388              
==========================================
- Hits        35719    35710       -9     
  Misses       2997     2997              
  Partials       56       56              

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[iuioiua]

Nice