feat(notification): adds theme variables for each type, fixed placement documentation example and corresponding to the placement margin

[blackawn]

1. 添加了一些通知类型的变量 border color headerTextColor descriptionTextColor actionTextColor
2. 修复了 placement 例子显示位置不对
3. 调整了 placement 为 top-left top-right bottom-left bottom-right 时，margin 左或右边距有一些多出的情况

[vercel]

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