opt: move some assignment cast execbuilder logic to init-time

Lookups for the `crdb_internal.assignment_cast` function properties and
overload are now performed once at init-time instead of for every
assignment cast built at execbuild-time.

Release note: None

Author: mgartner

pkg/sql/opt/exec/execbuilder/scalar.go

@@ -370,6 +370,13 @@ func (b *Builder) buildCast(ctx *buildScalarCtx, scalar opt.ScalarExpr) (tree.Ty
 	return tree.NewTypedCastExpr(input, cast.Typ), nil
 }
 
+const assnCastFnName = "crdb_internal.assignment_cast"
+
+var (
+	assnCastFuncRef                  = tree.WrapFunction(assnCastFnName)
+	assnCastProps, assnCastOverloads = builtinsregistry.GetBuiltinProperties(assnCastFnName)
+)
+
 // buildAssignmentCast builds an AssignmentCastExpr with input i and type T into
 // a built-in function call crdb_internal.assignment_cast(i, NULL::T).
 func (b *Builder) buildAssignmentCast(
@@ -388,21 +395,15 @@ func (b *Builder) buildAssignmentCast(
 		return input, nil
 	}
 
-	const fnName = "crdb_internal.assignment_cast"
-	funcRef, err := b.wrapBuiltinFunction(fnName)
-	if err != nil {
-		return nil, err
-	}
-	props, overloads := builtinsregistry.GetBuiltinProperties(fnName)
 	return tree.NewTypedFuncExpr(
-		funcRef,
+		assnCastFuncRef,
 		0, /* aggQualifier */
 		tree.TypedExprs{input, tree.NewTypedCastExpr(tree.DNull, cast.Typ)},
 		nil, /* filter */
 		nil, /* windowDef */
 		cast.Typ,
-		props,
-		&overloads[0],
+		assnCastProps,
+		&assnCastOverloads[0],
 	), nil
 }