Add union_extract scalar function

[gstvg]

Which issue does this PR close?

Closes #11081

What changes are included in this PR?

union_extract implementation, benchs and docs Add tables with union colum on the session context of sqllogictests

Are these changes tested?

Yes. Every branch of the function is assigned an id and tested referencing it's id Since it's not possible yet to create scalar unions in SQL, those cases are tested as unit tests

Are there any user-facing changes?

No