project directory structure

[mpiroc]

We are not consistent about how we organize our files.

• Why are some utilities in foo/utilities/, but others in foo/?
• What's the difference between src/lambda and src/shared? Why is there so much lambda-specific code in src/shared?
• Why is cloudformation.ts in a separate directory?
  • ✅ Why does it export a namespace, when we don't use namespaces anywhere else?
• What really belongs in sam/cli? Does anything belong in sam/?
• Where should test utilities live? i.e. should we separate test/shared/fooUtils.test.ts from test/shared/fooTestUtils.ts?
• Why is test/ a child of src/ instead of a sibling?
• etc.

We should design a consistent directory structure, document it in-repo, and apply it.

[awschristou]

Also for consideration:

• AWS Explorer code should be separated into its own folder