css variables 考虑加上 --amis 前缀，解决单个页面加载多套组件库变量冲突样式错乱问题

#### 是否关联于某个问题吗：
很多组件库都是默认使用 `--primary-color` 来命名 CSS 变量，导致加载多套组件库时会相互影响

#### 预期的解决方案：
有看到 ant-design 的解决方案是在 CSS variables 前面加了`--ant` 的前缀，如 `--ant-primary-color` ，参考 [ant-design css variables](https://github.com/ant-design/ant-design/blob/676a17038384df5607266db60597b00d7c4b5d86/scripts/css-variable-sync.js#L57)

No amis source file or test is named. Start by locating the CSS variable definitions and usages, then compare the referenced ant-design scripts/css-variable-sync.js approach. Done means variables are consistently prefixed so loading amis alongside another component library no longer causes cross-library style conflicts.

Written by the indexing model from the issue text.