Allow unresolved icon fallback to API/cdn mode

[jd-solanki]

Hi,

I am building Theme for third party developers where they can insert any icons for rendering this like. This same issue I described here: #544

I guess with new CDN option we can fallback to CDN mode when installed icon collection is not found.

assume, we have mdi collection installed and someone uses bx then Uno will fetch from cdn.

[antfu]

The CDN mode is for running UnoCSS in runtime with dynamic needs

• https://github.com/unocss/unocss#scanning
• https://github.com/unocss/unocss/tree/main/packages/runtime
• https://github.com/unocss/unocss/tree/main/packages/preset-icons#browser

[jd-solanki]

When we use cdn mode with regular nodejs mode, cdn mode takes over and all icons are fetched from API instead of first searching locally.

Feature request is the same behavior as how Iconify Icon component works. It first tries to fetch it from the registered collection and if collection is not found it fetches it from network/cdn.

Reproduction: https://codesandbox.io/s/uno-dynamic-icons-using-cdn-xndn5u

Previously you gave me a hint #544 (comment) but unfortunately I wasn't able to understand what you were referring to.

Regards.