chore: enable using the new toolkit from cli

[mrgrain]

Enable using the new Toolkit class from toolki-lib, inside the "old" CdkToolkit used by the CLI.

This will allow us to have new features be only implemented once with a thing pass through layer.

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 92.59259% with 4 lines in your changes missing coverage. Please review.

Project coverage is 85.42%. Comparing base (a9b456a) to head (952b711).

Files with missing lines	Patch %	Lines
packages/aws-cdk/lib/cli/cdk-toolkit.ts	94.44%	2 Missing ⚠️
packages/aws-cdk/lib/cxapp/cloud-executable.ts	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #311      +/-   ##
==========================================
- Coverage   85.80%   85.42%   -0.38%     
==========================================
  Files         169      219      +50     
  Lines       20524    24103    +3579     
  Branches     2304     2583     +279     
==========================================
+ Hits        17610    20590    +2980     
- Misses       2867     3462     +595     
- Partials       47       51       +4     

Flag	Coverage Δ
suite.unit	85.42% <92.59%> (-0.38%)	⬇️

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