feat(theme): allow custom icons in DocCard component

[jliermann]

Pre-flight checklist

• [x] I have read the Contributing Guidelines on pull requests.
• [x] If this is a code change: I have written unit tests and/or added dogfooding pages to fully verify the new behavior.
• [ ] If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

I had a project were I wanted to use the DocCard component from the theme with custom icons. I was able to swizzle it but considered that this addition might be of broader interest. The component accepts a property item.icon of type "string". It does currently not support image files but is also not broken by them.

Test Plan

I added a dogfooding doc under /tests/docs/doc-cards with different cases:

• Custom UTF emoji icon as string prop
• No custom icon (internal / external link)
• Several image files passed as props (unsupported)

Test links

Deploy preview: https://deploy-preview-11596--docusaurus-2.netlify.app/

Related issues/PRs

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[jliermann]

Thanks, @slorber, for the detailled and very helpful comments. I do understand that the scope of this change is too limited for merging. I will put some thought into how I can contribute to the feature requested in #7844.

[slorber]

Thanks

I think it would be better to open a RFC and once we agree on what should be done, open a new PR.

For now I'm closing this one