Agents - chat rendering in the chat content

[lszomoru]

Testing #333433

• Created a new chat as described in the TPI
• The chat bubble indicator at the end is not vertically centered

[vs-code-engineering]

Sharing media and context from merged PR #334083 for verification:

The global rendered-markdown codicon rule shifts icons down to align them with surrounding text. Rich links already manage their own icon alignment, but only the leading icon had its offset reset. This change also resets the trailing status icon, including while an agent chat link is temporarily rendered as a generic loading resource, and adds both in-progress chat and loading states to the existing rich-link component fixture.

Testing

• npm run stylelint -- src/vs/workbench/contrib/chat/browser/widget/chatContentParts/media/chatRichLink.css
• ./scripts/test.sh --run src/vs/workbench/contrib/chat/test/browser/widget/chatContentParts/chatRichLink.test.ts
• Verified in a live Agents window that both the pending chat status dot and the generic loading status dot share the exact vertical center with their content

Source PR: #334083