Improve readability of table scan projections in query plans

[andygrove]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
From discussion in #2690 (comment)

What about only showing the projection when there is one and ommiting it when there are none.
This could remove the None/Some too:

TableScan a projection=[col1,col2]

vs

TableScan a

Describe the solution you'd like
As above

Describe alternatives you've considered
None

Additional context
None

[LiuYuHui]

I’d like to try it.