fix(gatsby): cleanup fullySpecified resolving

[wardpeet]

Description

I did some more researching and we can disable fullySpecified in better way for all ESM modules. This allows us to skip fullySpecified on all js loaders.

How to test

import ky from "ky" inside your project to trigger this bug.

[karlhorky]

Is there an easy way to override the webpack config in Gatsby to enable fullySpecified? (eg. for users who want to opt in to full ESM with .js file extensions)

Ideally an easy to copy-paste example with two versions:

1. Opt in to fullySpecified everywhere
2. Opt in to fullySpecified for only some file(s) (eg. based on a pattern)

Then any users who are trying to do this can at least be pointed to the comment with the code examples in this PR.

[karlhorky]

I guess this could also have to do with the javascript/auto config?

Or maybe module: false or useESModule from Babel?

[karlhorky]

I guess according to the comment from @wardpeet, this should work out of the box:

We have tried the example above and we couldn't see the above error.

[karlhorky]

There may still be an issue with TypeScript though.

[wardpeet]

We would love to get a small reproduction and an issue to see where this is a problem.

[karlhorky]

Done, over here: #31077 (comment)

But I guess this actually may be a problem with webpack itself (or at least babel-loader and ts-loader):

webpack/webpack#13252