docs(svelte): add less alias import solution

[GRAMMAC1]

Summary

add less alias import solution to fix #5372

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[Copilot]

Pull Request Overview

This PR updates the Svelte plugin documentation by adding a solution for handling alias imports for LESS/SCSS files, addressing issue #5372.

• Added a new section on alias handling for both Chinese and English documentation.
• Provided an example configuration snippet for alias resolution using pluginSvelte.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
website/docs/zh/plugins/list/plugin-svelte.mdx	Added Chinese documentation for alias handling in LESS/SCSS with example configuration
website/docs/en/plugins/list/plugin-svelte.mdx	Added English documentation for alias handling in LESS/SCSS with example configuration

Comments suppressed due to low confidence (1)

website/docs/zh/plugins/list/plugin-svelte.mdx:144

• The documentation refers to 'preprocessor', but the code snippet uses 'preprocessOptions'. Please update the Chinese docs for consistency with the actual configuration option.

通过配置 `preprocessor` 可以保证在 Svelte 组件中引入的 `@import '@/styles/variables.scss` 或者 `@import '@/styles/variables.less'` 能够正确解析。

[chenjiahan]

Let's merge this PR first 😄