ESM specifier resolution flag does not use useESMLoader for entry point

[kennyr87]

The ES module specifier flag should use the esm loader to load extensionless entrypoints as esm modules. I believe the es-module-specifier-resolution option was deprecated in v13.4.0, but the esm loader is still using that option to specify the resolver: https://github.com/nodejs/node/blob/master/lib/internal/modules/run_main.js#L28

• Version: 14.7.0
• Platform: openSUSE Tumbleweed
• Subsystem: ESM Loader

What steps will reproduce the bug?

mkdir test-dir
cd test-dir
echo '{}' > package.json
touch entrypoint
touch test.mjs

/usr/bin/node --trace-warnings ./entrypoint test.mjs # <-- no error

/usr/bin/node --experimental-specifier-resolution=node --trace-warnings ./entrypoint test.mjs  <-- no error

How often does it reproduce? Is there a required condition?

Always

What is the expected behavior?

/usr/bin/node --experimental-specifier-resolution=node --trace-warnings ./entrypoint test.mjs

Should print the following to stdout:

internal/process/esm_loader.js:74
    internalBinding('errors').triggerUncaughtException(
                              ^

TypeError [ERR_INVALID_RETURN_PROPERTY_VALUE]: Expected string to be returned for the "format" from the "loader getFormat" function but got type object.
    at Loader.getFormat (internal/modules/esm/loader.js:110:13)
    at async Loader.getModuleJob (internal/modules/esm/loader.js:230:20)
    at async Loader.import (internal/modules/esm/loader.js:164:17)
    at async Object.loadESM (internal/process/esm_loader.js:68:5) {
  code: 'ERR_INVALID_RETURN_PROPERTY_VALUE'
}

What do you see instead?

/usr/bin/node --es-module-specifier-resolution=node --trace-warnings ./entrypoint test.mjs returns code: 'ERR_INVALID_RETURN_PROPERTY_VALUE'

I believe the es-module-specifier-resolution option was deprecated in v13.4.0

Additional information

https://github.com/nodejs/node/blob/master/lib/internal/modules/run_main.js#L28