Update workbench chat session list items to use pixel spinners

[hawkticehurst]

Align VS Code core workbench to agents window so chat session list items use the recently added pixel spinner instead of the static spinner codicon.

[vs-code-engineering]

Sharing media and context from merged PR #321814 for verification:

Updates workbench chat session list items, so active sessions use pixel spinner animation instead of static spinner codicon.

Note: When reduced motion is set, falls back to static spinner codicon.

Screen.Recording.2026-06-17.at.2.14.14.PM.mov

Source PR: #321814

[hogiSp]

during idle times, traffic lights could be displayed here - for "bridging" calls to prevent 10x Token costs due to cache expiry:
#321551

[DonJayamanne]

This is what i see