orm: support fn calls in where (#17127)

vlib/orm/orm_fn_calls_test.v

@@ -0,0 +1,48 @@
+import db.sqlite
+
+struct User {
+	id   int    [primary; sql: serial]
+	name string
+	age  int
+}
+
+fn get_acceptable_age() int {
+	return 21
+}
+
+fn test_fn_calls() {
+	mut db := sqlite.connect(':memory:') or { panic(err) }
+
+	sql db {
+		create table User
+	}
+
+	first_user := User{
+		name: 'first'
+		age: 25
+	}
+
+	second_user := User{
+		name: 'second'
+		age: 14
+	}
+
+	sql db {
+		insert first_user into User
+		insert second_user into User
+	}
+
+	users_with_acceptable_age := sql db {
+		select from User where age >= get_acceptable_age()
+	}
+
+	assert users_with_acceptable_age.len == 1
+	assert users_with_acceptable_age.first().name == 'first'
+
+	users_with_non_acceptable_age := sql db {
+		select from User where age < get_acceptable_age()
+	}
+
+	assert users_with_non_acceptable_age.len == 1
+	assert users_with_non_acceptable_age.first().name == 'second'
+}