add new devtools indicator loading state (#85083)
This removes the Next logo animation/dimming and replaces it with more
explicit states. We also use this UI to show when caches are being
warmed (when using Cache Components). When caches are being bypassed in
DevTools, we also will show this in the indicator with warning text,
indicating that we cannot accurately reflect what can be statically
prerendered.
https://github.com/user-attachments/assets/665d4f8b-8c01-4def-a60e-bc4ecdd1f879
