WHERE clause literals don't work

[mbutrovich]

WHERE clauses with literals are broken for a few reasons:

SELECT * FROM foo WHERE true (or false) explodes in codegen because these literals end up as a TypeCastExpression with a child ConstantValueExpression. There seems to be a recurring debate over where type casting and promotion should happen, and for now that means this breaks since no one handles it correctly. Other expressions that resolve to boolean (i.e. 5=5) work just fine.

SELECT FROM foo WHERE null explodes because NULL doesn't have a defined type on its own (they stay type::TypeId::INVALID). Maybe the binder can just change this to a boolean false since it would have the same effect? Not sure about that fix since it feels like a special-case hack. As above, and equally amusing, other expressions that resolve to null (i.e. 1=NULL) work just fine.

#1545 at least fixes the case for literals of invalid types.