Fix import resolving during staged contract updates

[SupunS]

Fixes part of onflow/cadence#3098 (comment)

The elaborations and the ContractAdditionHandler used for the contract update validator needs to be initialized using all payloads, not just with the payloads of the migrating account.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 88.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 55.93%. Comparing base (00f5b14) to head (722f220).

Files	Patch %	Lines
...il/ledger/migrations/staged_contracts_migration.go	88.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@                    Coverage Diff                     @@
##           feature/stable-cadence    #5551      +/-   ##
==========================================================
+ Coverage                   55.87%   55.93%   +0.05%     
==========================================================
  Files                        1049     1049              
  Lines                      103114   103119       +5     
==========================================================
+ Hits                        57618    57676      +58     
+ Misses                      41103    41057      -46     
+ Partials                     4393     4386       -7     

Flag	Coverage Δ
unittests	55.93% <88.00%> (+0.05%)	⬆️

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[turbolent]

Thank you for fixing this! I must have probably broke this at some point unknowingly, so thank you for also adding a test case 👌