Improve unnamed expressions

[Dandandan]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
To support optimizations like constant folding the column names need to keep consistent.

This is already visible at the (limited) constant folding we have:

> SELECT TRUE = TRUE;
+---------------+
| Boolean(true) |
+---------------+
| true          |
+---------------+
1 rows in set. Query took 0 seconds.

Describe the solution you'd like

Redesign DataFusion to handle unnamed expressions better.

Describe alternatives you've considered
Keep it as is - here the column names would changed based on the applied optimizations.

Additional context
#237