fix(emotion): Strip backslashed segments for Windows path

[iryan2]

Currently, when @swc/plugin-emotion is used on Windows, it produces invalid CSS class names. Apparently this is an unsolved issue for Rust. In this PR I've updated the calculation of the [filename] labelFormat such that it handles both the Windows path, which includes the full path to the file, including backslashes, and the Unix path (which was working fine to begin with).

I have set up a minimal repo for reproducing the issue and verifying the fix. The issue can be reproduced on the main branch, and the fix can be verified on the fix branch. The fix branch replaces the compiled swc_plugin_emotion.wasm from @swc/plugin-emotion npm package with one I built myself via my fork of this repo.

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After

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Fixes #327

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Latest commit: b1d2e0f

The changes in this PR will be included in the next version bump.

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Name	Type
@swc/plugin-emotion	Patch

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