Add a message streaming indicator in AI conversation #4060

All 531 tests pass, 4 skipped in 7m 22s

535 tests ±0 531 ✔️ ±0 7m 22s ⏱️ -11s
    1 suites ±0     4 💤 ±0
    1 files ±0     0 ❌ ±0

Results for commit f4c846e. ± Comparison against earlier commit 1265cb0.