exec: mixed type binary expressions and comparisons

[rafiss]

We need to handle mixed types in projection ops. For example:

root@127.0.0.1:60323/defaultdb> create table foo (a int4 primary key);
CREATE TABLE

root@127.0.0.1:60323/defaultdb> insert into foo values(1);
INSERT 1

root@127.0.0.1:60323/defaultdb> select a+1 from foo;
   ?column?
+------------+
  2
(1 row)

root@127.0.0.1:60323/defaultdb> set experimental_vectorize=always;
SET

root@127.0.0.1:60323/?> select a+1 from foo;
pq: unable to vectorize execution plan: unable to columnarize render expression "@1 + 1:::INT8": BinaryExpr on int4 and int is unhandled

There are a few different types of mixed type expressions to cover. We should probably implement them in this order:

• Comparison expressions. Only allow floats to be compared to to other float types, and ints to be compared to all other int types
• Allow all the mixed type comparisons, like int-float, int-decimal, etc.
• Binary expressions for plus, minus, and multiplication. Again, only mixed types should be float-float or int-int.
• All the mixed type expressions for plus, minus, and mult. (Might be easier to do at same time as above?)
• Binary expression for division. NOTE: currently the overloads do not implement the floor division // operator. start with that. (floor division work will be covered by exec: support //, %, and bitwise binary operators #40312)
• Then afterwards handle regular division with the / operator, which is not really done correctly right now.

Also, sometimes CastExpr is planned, and we will handle that in #39372