Notebooks: No visual indication that cells are pending on a cell in "Run by line" status

[ronglums]

Version: 1.63.0-insider (user setup)
Commit: ed3018f
Date: 2021-11-23T05:33:39.595Z
Electron: 13.5.2
Chromium: 91.0.4472.164
Node.js: 14.16.0
V8: 9.1.269.39-electron.0
OS: Windows_NT x64 10.0.22000

1. open an ipynb file
2. start "Run by line" in any of the cells
3. wait until "Run by line" finishes starting, i.e. cursor stops at the first line in the cell
4. perform "Run All"

Actual:
No cells are running because execution is pending on the cell in the "run by line" status, however there's no visual indication telling users that. It could be confusing as to why nothing is running.

[roblourens]

I think that #130611 (comment) will be the best solution to this