refactor resolverFunctions into their own file; should break this into
2x PRs later.

* Test coverage: add test case to confirm that moduleType overrides are applied for ts-node in loader mode

* Ensure that a default export exists for the esm-exception module

* Re-order tsconfig.json glob rules, and use implicit globbing

* lint fixup: apply prettier

* Add 'experimental-specifier-resolution' flag to NPM options in ESM module override test

* Ensure that a default export exists for the cjs-subdir module

* Revert "Ensure that a default export exists for the cjs-subdir module"

This reverts commit c64cf92.

* Revert "Add 'experimental-specifier-resolution' flag to NPM options in ESM module override test"

This reverts commit 1093df8.

* Specify tsconfig project using TS_NODE_PROJECT environment variable

* Use full file paths in preference to directory-default module imports

This avoids ERR_UNSUPPORTED_DIR_IMPORT, without having to provide the 'experimental-specifier-resolution' flag to ts-node

* Update index.ts

* Update index.ts

* Update tsconfig.json

* Extract execModuleTypeOverride function

* Add expected failure cases for Node 12.15, 14.13

Co-authored-by: Andrew Bradley <cspotcode@gmail.com>