Nextjs: Improve support for Windows-style paths

[T99]

Added more portable path handling code to better support win32-style paths. Prior to this PR, attempting to use fonts via `next/font/local' in Storybook on a Windows machine would result in broken font resource paths.

Closes #21968

What I did

Added more portable path handling code to better support win32-style paths. As demonstrated by #21968, a bug existed with the current way that paths were being translated between next/font and Storybook. This PR utilizes more portable path handling logic and sanitizes win32-style paths to the Unix-style paths expected in standard web URIs.

How to test

1. Open a story that uses fonts loaded via next/font on a Windows-based machine.
2. Check the @font-face declarations that are generated into the story and ensure that the paths are correct, and that the fonts are being loaded and are available in the story.

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli/src/sandbox-templates.ts
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "build", "documentation", "maintenance", "dependencies", "other"]

[yannbf]

Hey @ndelangen would you mind checking this out whenever you have time? Thanks!

It might take some time as we are quite busy, we really appreciate your efforts and patience <3

[ndelangen]

I do not have the capability to follow these manual testing steps, because I have no Windows based machine at my disposal.

I find it impossible to judge the code-change by looking at the diff alone.
I need to pass this to a maintainer that knows more about windows paths than me... @valentinpalkovic when you return, can you please look at this and review?

[valentinpalkovic]

Hey @T99,

Well done and thank you for the provided fix!

Tested on Windows and verified, whether it's still working in non-Windows environments