chore: migrate all remaining modules from NodeUnit to Jest (aws#16585)

Migrates `aws-cloudformation`, `cfnspec`, and `aws-codebuild` to jest.

In `aws-cloudformation`, jest does not like the idea of nested tests; however, as the scope of this PR is to migrate, I have added `eslint-ignore` to the relevant lines. The linter error in question is [valid-describe](https://github.com/jest-community/eslint-plugin-jest/blob/main/docs/rules/valid-describe.md). 

----

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

Author: kaizencc

packages/@aws-cdk/aws-cloudformation/.gitignore

@@ -15,4 +15,6 @@ nyc.config.js
 *.snk
 !.eslintrc.js
 
-junit.xml
+junit.xml
+
+!jest.config.js

packages/@aws-cdk/aws-cloudformation/.npmignore

@@ -24,4 +24,5 @@ tsconfig.json
 **/cdk.out
 junit.xml
 test/
-!*.lit.ts
+!*.lit.ts
+jest.config.js