Add a message streaming indicator in AI conversation #4065

All 532 tests pass, 4 skipped in 10m 11s

536 tests +1 532 ✔️ +1 10m 11s ⏱️ + 2m 5s
    1 suites ±0     4 💤 ±0
    1 files ±0     0 ❌ ±0

Results for commit 026f3f5. ± Comparison against earlier commit 8503965.