Language service does not support non-extension paths of JS files

[tzachbon]

There is a general issue when trying to resolve js files in the language service.
You would expect it to be similar to the webpack plugin path resolution.

I would expect the language service to "jump to file" when I click on the default import of the JS mixin for example, but it is not the case when the .js extension is missing, or even if it is an index file and you write the only the dirname.

Examples time -

Let's say I have 2 files next to each other:

- my-mixin.js
- style.st.css

In the style.st.css:

@st-import myMixin from "./my-mixin.js"

When clicking on the myMixin import it jumps to my-mixin.js as expected like this:

module.exports = function |myMixin([...]) {
	return {
		...
	};
}

The problem starts when I remove the extension to:

@st-import myMixin from "./my-mixin"

And when I hover, I get this error in the output of VSCode:

[Error - 12:31:00 PM] Request textDocument/definition failed.
  Message: Request textDocument/definition failed with message: ENOENT: no such file or directory, open '/Users/project/src/my-mixin'
  Code: -32603 

Note: when using this code with the webpack plugin, everything works as expected