CloudFormation: Allow deletion of deeply nested structures

[bblommers]

Scenario: Resource A depends on resource B

When CloudFormation tries to delete both resources, it will do so in an unspecified order.
If CF tries to delete resource B first, it will fail because A depends on it
CloudFormation continues with the deletion of resource A (and any other unrelated resources)

Because B is not yet deleted, CF will iterate over the remaining resources. Nothing depends on resource B anymore, so it will be deleted successfully.

This was already implemented, but with the caveat that we would only iterate over the list of remaining resources up to 5 times.

With this change, we will iterate as long as we are deleting some resources per iteration, i.e.: there is some progression. This has two benefits:

• Deletion of resources with a chain of 5 or more dependencies should now be successful (as we just keep retrying until everything is gone)
• If the deletion of a resource will never work, for whatever reason, we don't need to retry 5 times. Moto now immediately realizes that we haven't been able to delete any resources, and stop processing.

Related: #7381

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.77%. Comparing base (9aef694) to head (7f620e9).
Report is 63 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7413      +/-   ##
==========================================
- Coverage   95.88%   95.77%   -0.11%     
==========================================
  Files         843      843              
  Lines       82578    83096     +518     
==========================================
+ Hits        79178    79589     +411     
- Misses       3400     3507     +107     

Flag	Coverage Δ
servertests	32.49% <0.00%> (-0.03%)	⬇️
unittests	95.74% <100.00%> (-0.11%)	⬇️

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[github-actions]

This is now part of moto >= 5.0.3.dev34