JEST test support ES Module

Not yet ready: jest cannot run tests correctly in ESM mode and mocking in our tests will need rework. It's possible to have jest convert everything to CJS, however ESM-only features (e.g. import.meta.url) will then fail instead.

Ref:

- https://jestjs.io/docs/ecmascript-modules
- https://kulshekhar.github.io/ts-jest/docs/guides/esm-support/

Jest ESM support:

- https://github.com/facebook/jest/issues/9430
- https://github.com/nodejs/node/pull/31032
- https://github.com/kulshekhar/ts-jest/issues/1174
- https://github.com/kulshekhar/ts-jest/issues/1709
- https://github.com/facebook/jest/issues/12183#issuecomment-1004320665

Code:

- e6f29fb

Issue:

- https://stackoverflow.com/a/50052194/1334703
- https://nodejs.org/api/esm.html#esm_no_require_exports_module_exports_filename_dirname

Start by reviewing commit e6f29fb and the linked Jest and ts-jest ESM support documentation. Investigate how the current tests use mocking and ESM-only features such as import.meta.url. Done means Jest runs the test suite correctly in ESM mode without breaking those features or requiring incompatible mocking changes.

Written by the indexing model from the issue text.