test(e2e): rename folder for plugins

[chenjiahan]

Summary

Rename folder for plugins to make the structure of test cases clearer.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[Copilot]

Pull Request Overview

Renames and restructures E2E test case folders under plugin-less, plugin-babel, and assets to clarify plugin-based test layouts.

• Adds a plugin-less case to validate exclusion of specific Less files
• Splits and renames plugin-babel cases into basic and decorator, covering JS/TS decorators and custom Babel plugins
• Introduces a standalone SVG-assets case for URL-imported and CSS-referenced SVGs

Reviewed Changes

Copilot reviewed 293 out of 293 changed files in this pull request and generated no comments.

File	Description
e2e/cases/plugin-less/exclude-with-helper/src/*	New Less imports, helper config, and test for excluding b.less
e2e/cases/plugin-babel/decorator/src/* & config & tests	JS/TS decorator demo files, Babel plugin config, and E2E tests
e2e/cases/plugin-babel/basic/src & plugins & tests	Basic dynamic import case with a custom Babel plugin and exclusion
e2e/cases/assets/svg-assets/src/* & tests	SVG URL imports in JS and CSS, with Playwright assertions

Comments suppressed due to low confidence (1)