Make TaskContext wrap SessionState

[lewiszlw]

Is your feature request related to a problem or challenge?

I have a user defined table function FlattenTableFunc whice needs reading data from other table provider. To serialize execution plan FlattenExec, I can't put SessionState in it directly. So I have to reconstruct SessionState in FlattenExec::execute method.

Describe the solution you'd like

I see TaskContext is just part of SessionState. Could we just make TaskContext wrap SessionState?

Describe alternatives you've considered

No response

Additional context

No response