Move the resolveImport function from @feature-sliced/filesystem into the toolkit

[illright]

Blocked by #88 #107

That function is not specific to FSD, and it will be useful for other plugin developers, so might as well move it.

This will also help with #83

[illright]

Actually, not into the toolkit

[daniilsapa]

@illright
Why not into the toolkit? The discussion is about making it useful for plugin developers, isn't it?
Also, based on our recent discussion, wanted to add a point, so we don't forget. We need to improve that function to implement the capability to easily add custom extensions for module resolution like .vue, .svelte and more in the future.

[illright]

I think it shouldn't be in the toolkit because I think it should be tightly integrated with Steiger core for caching. In this way, it doesn't really make sense to move it into a separate package if it's tightly coupled