feat(watermark): fontColor follows the theme

[oljc]

Types of changes

• New feature
• Bug fix
• Enhancement
• Component style change
• Typescript definition change
• Documentation change
• Coding style change
• Refactoring
• Test cases
• Continuous integration
• Breaking change
• Others

Background and context

#2785
水印组件跟随主题变化

Solution

因为组件库相对固定的主题选择器body

通过观察器 useMutationObserver 来观察body上主题的变化来控制水印。并关闭了不必要的观察配置以最佳性能运作。

iShot_2023-11-12_14.46.38.mp4

How is the change tested?

Changelog

Component	Changelog(CN)	Changelog(EN)	Related issues
watermark	水印字体色跟随主题变化	watermark font color follows the theme	Close #2785

Checklist:

• Test suite passes (npm run test)
• Provide changelog for relevant changes (e.g. bug fixes and new features) if applicable.
• Changes are submitted to the appropriate branch (e.g. features should be submitted to feature branch and others
  should be submitted to main branch)

Other information