refactor(core): rename @aws-cdk/cdk to @aws-cdk/core

[eladb]

Rename the module @aws-cdk/cdk to @aws-cdk/core since this is a more suitable name for it.

Language-specific names:

• Python: aws_cdk.core (renamed)
• .NET: Amazon.CDK (not renamed)
• Java: only artifactId changed to core but package and groupId are still software.amazon.awscdk

This change completely deletes the @aws-cdk/cdk module from the repo as a temporary measure, to ensure there are no lingering references. A subsequent commit will introduce @aws-cdk/cdk as a deprecated package.

Fixed #2733

BREAKING CHANGE: The @aws-cdk/cdk module was renamed to @aws-cdk/core

• Python: The aws_cdk.cdk module was renamed to aws_cdk.core
• Java: The artifact cdk in groupId software.amazon.awscdk was renamed to core

---

TODO:

• Create a deprecated @aws-cdk/cdk module (maybe in a subsequent PR).

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[mergify]

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checklist:

• PR title type(scope): text
  • type: fix, feat, refactor go into CHANGELOG, chore is hidden
  • scope: name of module without aws- or cdk- prefix or postfix (e.g. s3 instead of aws-s3-deployment)
  • text: use all lower-case, do not end with a period, do not include issue refs
• PR Description
  • Rationale: describe rationale of change and approach taken
  • Issues: indicate issues fixed via: fixes #xxx or closes #xxx
  • Breaking?: last paragraph: BREAKING CHANGE: <describe what changed + link for details>
• Testing
  • Unit test added. Prefer to add a new test rather than modify existing tests
  • CLI or init templates change? Re-run/add CLI integration tests
• Documentation
  • README: update module README to describe new features
  • API docs: public APIs must be documented. Copy from official AWS docs when possible
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