fix: icon class name prefix cannot be reset back to arco

[Pivixl]

Types of changes

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

Background and context

In the following scenario:

<ConfigProvider prefixCls='framework-isolation'>
  <Button />
  <IconLeft />

  <ConfigProvider prefixCls='arco'>
    <Button />
    <IconLeft />
  </ConfigProvider>

</ConfigProvider>

What to expect:

<ConfigProvider prefixCls='framework-isolation'>
  <button class="framework-isolation-button" />
  <svg class="framework-isolation-icon" />

  <ConfigProvider prefixCls='arco'>
    <button class="arco-button" />
    <svg class="arco-icon" />
  </ConfigProvider>

</ConfigProvider>

What actrually got:

<ConfigProvider prefixCls='framework-isolation'>
  <button class="framework-isolation-button" />
  <svg class="framework-isolation-icon" />

  <ConfigProvider prefixCls='arco'>
    <button class="arco-button" />
    <svg class="framework-isolation-icon" />
  </ConfigProvider>

</ConfigProvider>

The icon's class name prefix can never be set back to "arco"

Solution

How is the change tested?

Changelog

Component	Changelog(CN)	Changelog(EN)	Related issues
		fix: icon class name prefix cannot be reset back to arco

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)

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[yinkaihui]

这里需要对 prefixCls 判空下

[Pivixl]

这个是必要的吗？如果 prefixCls 没有传入或者是 undefined，它会被前面的 useMergeProps 改写回 'arco'，如果它是空字符串或其他假值，整体会跟随 arco 的其他组件变成 '-icon', 'null-icon', 'NaN-icon'，搭配修改 less 的 '@Prefix'，这些 icon 才有样式