feat: support config the scss variables

[tolking]

close #66, close #112

Add the themeChalk prop to configuring the SCSS variable. Only effective when importStyle is scss.

After configuration, a corresponding custom theme will be automatically generated to replace the original style.

What is the difference between this and manually configuring it yourself?

The only difference is the file path

// index.scss
- @forward 'element-plus/theme-chalk/src/common/var.scss' with (
+ @forward '/<rootDir>/node_modules/element-plus/theme-chalk/src/common/var.scss' with (

// nuxt.config.ts
- additionalData: `@use "@/assets/scss/element/index.scss" as element;`,
+ additionalData: `@use "/<rootDir>/.nuxt/index.scss" as element;`,

This kind of change can avoid some errors. e.g. #161, #131