Cascade Layers support

[tim-richter]

Hi! 👋

Firstly, thanks for your work on this project! 🙂

Since antd introduced a way to apply cascade layers to their styles (https://ant.design/docs/react/compatible-style#layer-downgrade), I was wondering, if we could support this for the icons as well.

Currently all of the injected styles from this library would have a higher specificity, then antd styles, if used together with layer. This could cause specificity issues in the long run.
It would also make it easier for antd users, to use icons in their projects, if those would automatically get the same specificity layer as antd styles.

I could see two possible solutions to this:

• Letting the IconContext set this for all icons and then using the context to conditionally wrap the iconStyles with the antd layer (probably easiest to do)
• Applying the styles from this repo via @ant-design/css-in-js. Since we have to set layer already on the @ant-design/css-in-js, this should make sure the layer is also applied to the icons as well.

Let me know which solutions would work best and if I can help with any of those.