added submodule tests

[iambumblehead]

adds tests and changes for subpath exports, tests the export patterns from the documentation site https://nodejs.org/api/packages.html#package-entry-points

{
  "exports": {
    ".": "./index.js",
    "./submodule.js": "./src/submodule.js"
  }
}

[iambumblehead]

this will not be ready tonight/today

[iambumblehead]

parts of PACKAGE_RESOLVE(packageSpecifier, parentURL) from https://nodejs.org/api/esm.html need to be followed

scoped packages would be affected so scoped package tests should be added to the main test file

[iambumblehead]

tests are passing, but a few extra things are needed,

• the subpath lookup needs to be updated to handle subpath globby patterns,
• one esm export lookup should be shared/reused by for subpath lookups and package man/index lookups
• probably, the export lookup should recursively process export lists and object definitions
• tests and support should be added for "#subpath"

[iambumblehead]

the "index.js" files should be renamed eg "index.test.js" so they won't be returned through legacy cjs-resolving functions where "index.js" is automatically returned.

[aladdin-add]

nits: the func name is really hard to read. lol.

[iambumblehead]

haha ok

[iambumblehead]

this was renamed to "esmparseimportpkg" if you prefer a different name it could be changed and readability improvements could be made in a follow up PR

[iambumblehead]

note to myself mostly. resolvewithplus should be updated to return file urls like 'file:///path/to/script.js' and 'node:fs' to match the import.meta.resolve behaviour and to save esmock from the need to check if protocol is defined or to add the protocol

[iambumblehead]

Everything is working here and the tests are passing.

A few refinements that could be made but haven't been made yet,

• reuse one parsing function for both import and export patterns,
• remove export pattern parsing from the cjs package.json filepaths resolving function,
• improve function names and variable names or readability

I don't know when these improvements will be made. This is a dull task and my energy is low atm.

[iambumblehead]

tests for these nested and conditional export definitions should be added as well :/

https://nodejs.org/api/packages.html#conditional-exports

{
  "exports": {
    ".": "./index.js",
    "./feature.js": {
      "node": "./feature-node.js",
      "default": "./feature.js"
    }
  }
}

https://nodejs.org/api/packages.html#conditional-exports

{
  "exports": {
    "node": {
      "import": "./feature-node.mjs",
      "require": "./feature-node.cjs"
    },
    "default": "./feature.mjs"
  }
}

[iambumblehead]

one function is now used to parse spec patterns to obtain,

1. package root index,
2. getting a package's exported specifier and
3. getting a package's imported specifier

it will be ready for review after tests for the patterns above are added and function names are improved.

[iambumblehead]

@tripodsan @aladdin-add this PR may be too annoying to review. It has become a huge PR. If you will review this that's great and if not it is understood why.

Some function names are changed a little bit, but imo it would be easier to refine things more in a follow up PR. There is something off about linting and/or my editor that needs to be looked into and probably we should remove the "o.functioname" pattern and use something like "const functionName" or whatever.

This PR completes the objective of resolving esm patterns from node.js' documentation examples

[iambumblehead]

merging this!